PHP Coding Standard

PHP Coding Standard

For newer PHP coding standards please see:

• Zend Framework Coding Standard for PHP
• Basic Coding Standard from PHP FIG
• Coding Style Guide from PHP FIG
• PEAR Coding Standards

Or if you need help with PHP, contact TodaysWeb.

This PHP Coding Standard is with permission based on Todd Hoff's C++ Coding Standard.
Rewritten for PHP by Fredrik Kristiansen / DB Medialab, Oslo 2000-2003.

Last Modified: 2003-02-17

Contents

• Introduction
  • Standardization is Important
  • Interpretation
  • Accepting an Idea
• Names
  • Make Names Fit
  • No All Upper Case Abbreviations
  • Class Names
  • Class Library Names
  • Method Names
  • Class Attribute Names
  • Method Argument Names
  • Variable Names
  • Array Element
  • Reference Variables and Functions Returning References
  • Global Variables
  • Define Names and Global Constants
  • Static Variables
  • Function Names

• Documentation
  • Comments on Comments
  • Comments Should Tell a Story
  • Document Decisions
  • Use Headers
  • Make Gotchas Explicit
  • Interface and Implementation Documentation
  • Directory Documentation

• Complexity Management
  • Layering
  • Open/Closed Principle
• Classes
  • Different Accessor Styles
  • Do Not do Real Work in Object Constructors
  • Thin vs. Fat Class Interfaces
  • Short Methods

• Process
  • Code Reviews
  • Create a Source Code Control System Early and Not Often
  • Create a Bug Tracking System Early and Not Often
  • Honor Responsibilities

• Formatting
  • Brace {} Policy
  • Indentation/Tabs/Space Policy
  • Parens () with Key Words and Functions Policy
  • If Then Else Formatting
  • switch Formatting
  • Use of continue,break and ?:
  • One Statement Per Line
  • Alignment of Declaration Blocks

• Server configuration
  • HTTP_*_VARS
  • PHP File Extensions

• Miscellaneous
  • PHP Code Tags
  • No Magic Numbers
  • Error Return Check Policy
  • Do Not Default If Test to Non-Zero
  • The Bull of Boolean Types
  • Usually Avoid Embedded Assignments
  • Reusing Your Hard Work and the Hard Work of Others
  • Use if (0) to Comment Out Code Blocks

Introduction

Standardization is Important

It helps if the standard annoys everyone in some way so everyone feels they are on the same playing field. The proposal here has evolved over many projects, many companies, and literally a total of many weeks spent arguing. It is no particular person's style and is certainly open to local amendments.

Good Points

When a project tries to adhere to common standards a few good things happen:

• programmers can go into any code and figure out what's going on
• new people can get up to speed quickly
• people new to PHP are spared the need to develop a personal style and defend it to the death
• people new to PHP are spared making the same mistakes over and over again
• people make fewer mistakes in consistent environments
• programmers have a common enemy :-)

Bad Points

Now the bad:

• the standard is usually stupid because it was made by someone who doesn't understand PHP
• the standard is usually stupid because it's not what I do
• standards reduce creativity
• standards are unnecessary as long as people are consistent
• standards enforce too much structure
• people ignore standards anyway

Discussion

The experience of many projects leads to the conclusion that using coding standards makes the project go smoother. Are standards necessary for success? Of course not. But they help, and we need all the help we can get! Be honest, most arguments against a particular standard come from the ego. Few decisions in a reasonable standard really can be said to be technically deficient, just matters of taste. So be flexible, control the ego a bit, and remember any project is fundamentally a team effort.

Interpretation

Conventions

The use of the word "should" directs projects in tailoring a project-specific standard, in that the project must include, exclude, or tailor the requirement, as appropriate.

The use of the word "may" is similar to "should", in that it designates optional requirements.

Standards Enforcement

First, any serious concerns about the standard should be brought up and worked out within the group. Maybe the standard is not quite appropriate for your situation. It may have overlooked important issues or maybe someone in power vehemently disagrees with certain issues :-)

In any case, once finalized hopefully people will play the adult and understand that this standard is reasonable, and has been found reasonable by many other programmers, and therefore is worthy of being followed even with personal reservations.

Failing willing cooperation it can be made a requirement that this standard must be followed to pass a code inspection.

Failing that the only solution is a massive tickling party on the offending party.

Accepting an Idea

1. It's impossible.
2. Maybe it's possible, but it's weak and uninteresting.
3. It is true and I told you so.
4. I thought of it first.
5. How could it be otherwise.

If you come to objects with a negative preconception please keep an open mind. You may still conclude objects are bunk, but there's a road you must follow to accept something different. Allow yourself to travel it for a while.

Names

Make Names Fit

Names are the heart of programming. In the past people believed knowing someone's true name gave them magical power over that person. If you can think up the true name for something, you give yourself and the people coming after power over the code. Don't laugh!

A name is the result of a long deep thought process about the ecology it lives in. Only a programmer who understands the system as a whole can create a name that "fits" with the system. If the name is appropriate everything fits together naturally, relationships are clear, meaning is derivable, and reasoning from common human expectations works as expected.

If you find all your names could be Thing and DoIt then you should probably revisit your design.

Class Names

• Name the class after what it is. If you can't think of what it is that is a clue you have not thought through the design well enough.
• Compound names of over three words are a clue your design may be confusing various entities in your system. Revisit your design. Try a CRC card session to see if your objects have more responsibilities than they should.
• Avoid the temptation of bringing the name of the class a class derives from into the derived class's name. A class should stand on its own. It doesn't matter what it derives from.
• Suffixes are sometimes helpful. For example, if your system uses agents then naming something DownloadAgent conveys real information.

Method and Function Names

• Usually every method and function performs an action, so the name should make clear what it does: CheckForErrors() instead of ErrorCheck(), DumpDataToFile() instead of DataFile(). This will also make functions and data objects more distinguishable.
• Suffixes are sometimes useful:
  • Max - to mean the maximum value something can have.
  • Cnt - the current count of a running count variable.
  • Key - key value.

  For example: RetryMax to mean the maximum number of retries, RetryCnt to mean the current retry count.

• Prefixes are sometimes useful:
  • Is - to ask a question about something. Whenever someone sees Is they will know it's a question.
  • Get - get a value.
  • Set - set a value.

  For example: IsHitRetryLimit.

No All Upper Case Abbreviations

• When confronted with a situation where you could use an all upper case abbreviation instead use an initial upper case letter followed by all lower case letters. No matter what.
  
  Do use: GetHtmlStatistic.
  Do not use: GetHTMLStatistic.
  

Justification

• People seem to have very different intuitions when making names containing abbreviations. It's best to settle on one strategy so the names are absolutely predictable.

  Take for example NetworkABCKey. Notice how the C from ABC and K from key are confused. Some people don't mind this and others just hate it so you'll find different policies in different code so you never know what to call something.

Example

   class FluidOz             // NOT FluidOZ
   class GetHtmlStatistic       // NOT GetHTMLStatistic

Class Names

• Use upper case letters as word separators, lower case for the rest of a word
• First character in a name is upper case
• No underbars ('_')

Justification

• Of all the different naming strategies many people found this one the best compromise.

Example

   class NameOneTwo

   class Name

Class Library Names

• Now that name spaces are becoming more widely implemented, name spaces should be used to prevent class name conflicts among libraries from different vendors and groups.
• When not using name spaces, it's common to prevent class name clashes by prefixing class names with a unique string. Two characters is sufficient, but a longer length is fine.

Example

John Johnson's complete data structure library could use JJ as a prefix, so classes would be:

   class JjLinkList
   {
   }

Method Names

• Use the same rule as for class names.

Justification

• Of all the different naming strategies many people found this one the best compromise.

Example

   class NameOneTwo
   {
      function DoIt() {};
      function HandleError() {};
   }

Class Attribute Names

• Class member attribute names should be prepended with the character 'm'.
• After the 'm' use the same rules as for class names.
• 'm' always precedes other name modifiers like 'r' for reference.

Justification

• Prepending 'm' prevents any conflict with method names. Often your methods and attribute names will be similar, especially for accessors.

Example

   class NameOneTwo
   {
      function VarAbc() {};
      function ErrorNumber() {};
      var $mVarAbc;
      var $mErrorNumber;
      var $mrName;
   }

Method Argument Names

• The first character should be lower case.
• All word beginnings after the first letter should be upper case as with class names.

Justification

• You can always tell which variables are passed in variables.

Example

   class NameOneTwo
   {
      function StartYourEngines(&$someEngine, &$anotherEngine) {
        $this->mSomeEngine = $someEngine;
        $this->mAnotherEngine = $anotherEngine;
      }

      var $mSomeEngine;
      var $mAnotherEngine;
   }

Variable Names

• use all lower case letters
• use '_' as the word separator.

Justification

• With this approach the scope of the variable is clear in the code.
• Now all variables look different and are identifiable in the code.

Example

function HandleError($errorNumber)
{
    $error = new OsError;
    $time_of_error = $error->GetTimeOfError();
    $error_processor = $error->GetErrorProcessor();
}

Array Element

Array element names follow the same rules as a variable.

• use '_' as the word separator.
• don't use '-' as the word separator

Justification

• if '-' is used as a word separator it will generate warnings used with magic quotes.

Example

$myarr['foo_bar'] = 'Hello';
print "$myarr[foo_bar] world"; // will output: Hello world

$myarr['foo-bar'] = 'Hello';
print "$myarr[foo-bar] world"; // warning message

Single or Double Quotes

• Access an array's elements with single or double quotes.
• Don't use quotes within magic quotes

Justification

• Some PHP configurations will output warnings if arrays are used without quotes except when used within magic quotes

Example

$myarr['foo_bar'] = 'Hello';
$element_name = 'foo_bar';
print "$myarr[foo_bar] world"; // will output: Hello world
print "$myarr[$element_name] world"; // will output: Hello world
print "$myarr['$element_name'] world"; // parse error
print "$myarr["$element_name"] world"; // parse error

Reference Variables and Functions Returning References

• References should be prepended with 'r'.

Justification

• The difference between variable types is clarified.
• It establishes the difference between a method returning a modifiable object and the same method name returning a non-modifiable object.

Example

class Test
{
    var $mrStatus;
    function DoSomething(&$rStatus) {};
    function &rStatus() {};
}

Global Variables

• Global variables should be prepended with a 'g'.

Justification

• It's important to know the scope of a variable.

Example

    global $gLog;
    global &$grLog;

Define Names / Global Constants

• Global constants should be all caps with '_' separators.

Justification

It's tradition for global constants to named this way. You must be careful to not conflict with other predefined globals.

Example

define("A_GLOBAL_CONSTANT", "Hello world!");

Static Variables

• Static variables may be prepended with 's'.

Justification

• It's important to know the scope of a variable.

Example

function test()
{
  static $msStatus = 0;
}

Function Names

• For PHP functions use the C GNU convention of all lower case letters with '_' as the word delimiter.

Justification

• It makes functions very different from any class related names.

Example

function some_bloody_function()
{
}

Error Return Check Policy

• Check every system call for an error return, unless you know you wish to ignore errors.
• Include the system error text for every system error message.

Braces {} Policy

Of the three major brace placement strategies two are acceptable, with the first one listed being preferable:

• Place brace under and inline with keywords:

  
     if ($condition)       while ($condition)
     {                     {
        ...                   ...
     }                     }
  

• Traditional Unix policy of placing the initial brace on the same line as the keyword and the trailing brace inline on its own line with the keyword:

  
     if ($condition) {     while ($condition) {
        ...                   ...
     }                     }
  

Justification

• Another religious issue of great debate solved by compromise. Either form is acceptable, many people, however, find the first form more pleasant. Why is the topic of many psychological studies.

  There are more reasons than psychological for preferring the first style. If you use an editor (such as vi) that supports brace matching, the first is a much better style. Why? Let's say you have a large block of code and want to know where the block ends. You move to the first brace hit a key and the editor finds the matching brace. Example:

  
       if ($very_long_condition && $second_very_long_condition)
       {
          ...
       }
       else if (...)
       {
      ...
       }
  

  To move from block to block you just need to use cursor down and your brace matching key. No need to move to the end of the line to match a brace then jerk back and forth.

Indentation/Tabs/Space Policy

• Indent using 4 spaces for each level.
• Do not use tabs, use spaces. Most editors can substitute spaces for tabs.
• Indent as much as needed, but no more. There are no arbitrary rules as to the maximum indenting level. If the indenting level is more than 4 or 5 levels you may think about factoring out code.

Justification

• When people using different tab settings the code is impossible to read or print, which is why spaces are preferable to tabs.
• Most PHP applications use 4 spaces.
• Most editors use 4 spaces by defalt.
• As much as people would like to limit the maximum indentation levels it never seems to work in general. We'll trust that programmers will choose wisely how deep to nest code.

Example

   function func()
   {
      if (something bad)
      {
         if (another thing bad)
         {
            while (more input)
            {
            }
         }
      }
   }

Parens () with Key Words and Functions Policy

• Do not put parens next to keywords. Put a space between.
• Do put parens next to function names.
• Do not use parens in return statements when it's not necessary.

Justification

• Keywords are not functions. By putting parens next to keywords keywords and function names are made to look alike.

Example

    if (condition)
    {
    }

    while (condition)
    {
    }

    strcmp($s, $s1);

    return 1;

Do Not do Real Work in Object Constructors

Do not do any real work in an object's constructor. Inside a constructor initialize variables only and/or do only actions that can't fail.

Create an Open() method for an object which completes construction. Open() should be called after object instantiation.

Justification

• Constructors can't return an error.

Example

   class Device
   {
      function Device()    { /* initialize and other stuff */ }
      function Open()  { return FAIL; }
   };

   $dev = new Device;
   if (FAIL == $dev->Open()) exit(1);

Make Functions Reentrant

Functions should not keep static variables that prevent a function from being reentrant.

If Then Else Formatting

Layout

It's up to the programmer. Different bracing styles will yield slightly different looks. One common approach is:

   if (condition)                 // Comment
   {
   }
   else if (condition)            // Comment
   {
   }
   else                           // Comment
   {
   }

If you have else if statements then it is usually a good idea to always have an else block for finding unhandled cases. Maybe put a log message in the else even if there is no corrective action taken.

Condition Format

Always put the constant on the left hand side of an equality/inequality comparison. For example:

if ( 6 == $errorNum ) ...

One reason is that if you leave out one of the = signs, the parser will find the error for you. A second reason is that it puts the value you are looking for right up front where you can find it instead of buried at the end of your expression. It takes a little time to get used to this format, but then it really gets useful.

switch Formatting

• Falling through a case statement into the next case statement shall be permitted as long as a comment is included.
• The default case should always be present and trigger an error if it should not be reached, yet is reached.
• If you need to create variables put all the code in a block.

Example

   switch (...)
   {
      case 1:
         ...
      // FALL THROUGH

      case 2:
      {
         $v = get_week_number();
         ...
      }
      break;

      default:
   }

Use of continue,break and ?:

Continue and Break

Continue and break are really disguised gotos so they are covered here.

Continue and break like goto should be used sparingly as they are magic in code. With a simple spell the reader is beamed to god knows where for some usually undocumented reason.

The two main problems with continue are:

• It may bypass the test condition
• It may bypass the increment/decrement expression

Consider the following example where both problems occur:

while (TRUE)
{
   ...
   // A lot of code
   ...
   if (/* some condition */) {
      continue;
   }
   ...
   // A lot of code
   ...
   if ( $i++ > STOP_VALUE) break;
}

Note: "A lot of code" is necessary in order that the problem cannot be caught easily by the programmer.

From the above example, a further rule may be given: Mixing continue with break in the same loop is a sure way to disaster.

?:

The trouble is people usually try and stuff too much code in between the ? and :. Here are a couple of clarity rules to follow:

• Put the condition in parens so as to set it off from other code
• If possible, the actions for the test should be simple functions.
• Put the action for the then and else statement on a separate line unless it can be clearly put on one line.

Example

   (condition) ? funct1() : func2();

   or

   (condition)
      ? long statement
      : another long statement;

Alignment of Declaration Blocks

• Block of declarations should be aligned.

Justification

• Clarity.

• Similarly blocks of initialization of variables should be tabulated.

• The ‘&’ token should be adjacent to the type, not the name.

Example

   var       $mDate
   var&      $mrDate
   var&      $mrName
   var       $mName

   $mDate    = 0;
   $mrDate   = NULL;
   $mrName   = 0;
   $mName    = NULL;

One Statement Per Line

There should be only one statement per line unless the statements are very closely related.

Short Methods

• Methods should limit themselves to a single page of code.

Justification

• The idea is that the each method represents a technique for achieving a single objective.
• Most arguments of inefficiency turn out to be false in the long run.
• True function calls are slower than not, but there needs to a thought out decision (see premature optimization).

Document Null Statements

Always document a null body for a for or while statement so that it is clear that the null body is intentional and not missing code.

   while ($dest++ = $src++)
      ;         // VOID

Do Not Default If Test to Non-Zero

Do not default the test for non-zero, i.e.

   if (FAIL != f())

is better than

   if (f())

even though FAIL may have the value 0 which PHP considers to be false. An explicit test will help you out later when somebody decides that a failure return should be -1 instead of 0. Explicit comparison should be used even if the comparison value will never change; e.g., if (!($bufsize % strlen($str))) should be written instead as if (0 == ($bufsize % strlen($str))) to reflect the numeric (not boolean) nature of the test. A frequent trouble spot is using strcmp to test for string equality, where the result should never ever be defaulted.

The non-zero test is often defaulted for predicates and other functions or expressions which meet the following restrictions:

• Returns 0 for false, nothing else.
• Is named so that the meaning of (say) a true return is absolutely obvious. Call a predicate IsValid(), not CheckValid().

The Bull of Boolean Types

Do not check a boolean value for equality with 1 (TRUE, YES, etc.); instead test for inequality with 0 (FALSE, NO, etc.). Most functions are guaranteed to return 0 if false, but only non-zero if true. Thus,

   if (TRUE == func()) { ...

must be written

   if (FALSE != func()) { ...

Usually Avoid Embedded Assignments

There is a time and a place for embedded assignment statements. In some constructs there is no better way to accomplish the results without making the code bulkier and less readable.

   while ($a != ($c = getchar()))
   {
      process the character
   }

The ++ and -- operators count as assignment statements. So, for many purposes, do functions with side effects. Using embedded assignment statements to improve run-time performance is also possible. However, one should consider the tradeoff between increased speed and decreased maintainability that results when embedded assignments are used in artificial places. For example,

   $a = $b + $c;
   $d = $a + $r;

should not be replaced by

   $d = ($a = $b + $c) + $r;

even though the latter may save one cycle. In the long run the time difference between the two will decrease as the optimizer gains maturity, while the difference in ease of maintenance will increase as the human memory of what's going on in the latter piece of code begins to fade.

Reusing Your Hard Work and the Hard Work of Others

Reuse across projects is almost impossible without a common framework in place. Objects conform to the services available to them. Different projects have different service environments making object reuse difficult.

Developing a common framework takes a lot of up front design effort. When this effort is not made, for whatever reasons, there are several techniques one can use to encourage reuse:

Don't be Afraid of Small Libraries

One common enemy of reuse is people not making libraries out of their code. A reusable class may be hiding in a program directory and will never have the thrill of being shared because the programmer won't factor the class or classes into a library.

One reason for this is because people don't like making small libraries. There's something about small libraries that doesn't feel right. Get over it. The computer doesn't care how many libraries you have.

If you have code that can be reused and can't be placed in an existing library then make a new library. Libraries don't stay small for long if people are really thinking about reuse.

If you are afraid of having to update makefiles when libraries are recomposed or added then don't include libraries in your makefiles, include the idea of services. Base level makefiles define services that are each composed of a set of libraries. Higher level makefiles specify the services they want. When the libraries for a service change only the lower level makefiles will have to change.

Keep a Repository

Most companies have no idea what code they have. And most programmers still don't communicate what they have done or ask for what currently exists. The solution is to keep a repository of what's available.

In an ideal world a programmer could go to a web page, browse or search a list of packaged libraries, taking what they need. If you can set up such a system where programmers voluntarily maintain such a system, great. If you have a librarian in charge of detecting reusability, even better.

Another approach is to automatically generate a repository from the source code. This is done by using common class, method, library, and subsystem headers that can double as man pages and repository entries.

Comments on Comments

Comments Should Tell a Story

Consider your comments a story describing the system. Expect your comments to be extracted by a robot and formed into a man page. Class comments are one part of the story, method signature comments are another part of the story, method arguments another part, and method implementation yet another part. All these parts should weave together and inform someone else at another point of time just exactly what you did and why.

Document Decisions

Comments should document decisions. At every point where you had a choice of what to do place a comment describing which choice you made and why. Archeologists will find this the most useful information.

Use Headers

Use a document extraction system like ccdoc . Other sections in this document describe how to use ccdoc to document a class and method.

These headers are structured in such a way as they can be parsed and extracted. They are not useless like normal headers. So take time to fill them out. If you do it right once no more documentation may be necessary.

Comment Layout

Each part of the project has a specific comment layout.

Make Gotchas Explicit

Explicitly comment variables changed out of the normal control flow or other code likely to break during maintenance. Embedded keywords are used to point out issues and potential problems. Consider a robot will parse your comments looking for keywords, stripping them out, and making a report so people can make a special effort where needed.

Gotcha Keywords

• :TODO: topic
  Means there's more to do here, don't forget.

• :BUG: [bugid] topic
  means there's a Known bug here, explain it and optionally give a bug ID.

• :KLUDGE:
  When you've done something ugly say so and explain how you would do it differently next time if you had more time.

• :TRICKY:
  Tells somebody that the following code is very tricky so don't go changing it without thinking.

• :WARNING:
  Beware of something.

• :PARSER:
  Sometimes you need to work around a parser problem. Document it. The problem may go away eventually.

• :ATTRIBUTE: value
  The general form of an attribute embedded in a comment. You can make up your own attributes and they'll be extracted.

Gotcha Formatting

• Make the gotcha keyword the first symbol in the comment.
• Comments may consist of multiple lines, but the first line should be a self-containing, meaningful summary.
• The writer's name and the date of the remark should be part of the comment. This information is in the source repository, but it can take a quite a while to find out when and by whom it was added. Often gotchas stick around longer than they should. Embedding date information allows other programmer to make this decision. Embedding who information lets us know who to ask.

Example

   // :TODO: tmh 960810: possible performance problem
   // We should really use a hash table here but for now we'll
   // use a linear search.

   // :KLUDGE: tmh 960810: possible unsafe type cast
   // We need a cast here to recover the derived type. It should
   // probably use a virtual method or template.

See Also

See Interface and Implementation Documentation for more details on how documentation should be laid out.

Interface and Implementation Documentation

There are two main audiences for documentation:

• Class Users
• Class Implementors

With a little forethought we can extract both types of documentation directly from source code.

Class Users

Class users need class interface information which when structured correctly can be extracted directly from a header file. When filling out the header comment blocks for a class, only include information needed by programmers who use the class. Don't delve into algorithm implementation details unless the details are needed by a user of the class. Consider comments in a header file a man page in waiting.

Class Implementors

Class implementors require in-depth knowledge of how a class is implemented. This comment type is found in the source file(s) implementing a class. Don't worry about interface issues. Header comment blocks in a source file should cover algorithm issues and other design decisions. Comment blocks within a method's implementation should explain even more.

Directory Documentation

Every directory should have a README file that covers:

• the purpose of the directory and what it contains
• a one line comment on each file. A comment can usually be extracted from the NAME attribute of the file header.
• cover build and install directions
• direct people to related resources:
  • directories of source
  • online documentation
  • paper documentation
  • design documentation
• anything else that might help someone

Consider a new person coming in 6 months after every original person on a project has gone. That lone scared explorer should be able to piece together a picture of the whole project by traversing a source directory tree and reading README files, Makefiles, and source file headers.

Open/Closed Principle

The Open/Closed principle states a class must be open and closed where:

• open means a class has the ability to be extended.
• closed means a class is closed for modifications other than extension. The idea is once a class has been approved for use having gone through code reviews, unit tests, and other qualifying procedures, you don't want to change the class very much, just extend it.

The Open/Closed principle is a pitch for stability. A system is extended by adding new code not by changing already working code. Programmers often don't feel comfortable changing old code because it works! This principle just gives you an academic sounding justification for your fears :-)

In practice the Open/Closed principle simply means making good use of our old friends abstraction and polymorphism. Abstraction to factor out common processes and ideas. Inheritance to create an interface that must be adhered to by derived classes.

Server configuration

This section contains some guidelines for PHP/Apache configuration.

HTTP_*_VARS

HTTP_*_VARS are either enabled or disabled. When enabled all variables must be accessed through $HTTP_*_VARS[key]. When disabled all variables can be accessed by the key name.

• use HTTP_*_VARS when accessing variables.
• use enabled HTTP_*_VARS in PHP configuration.

Justification

• HTTP_*_VARS is available in any configuration.
• HTTP_*_VARS will not conflict with exsisting variables.
• Users can't change variables by passing values.

PHP File Extensions

There is lots of different extension variants on PHP files (.html, .php, .php3, .php4, .phtml, .inc, .class...).

• Always use the extension .php.
• Always use the extension .php for your class and function libraries.

Justification

• The use of .php makes it possible to enable caching on other files than .php.
• The use of .inc or .class can be a security problem. On most servers these extensions aren't set to be run by a parser. If these are accessed they will be displayed in clear text.

Miscellaneous

This section contains some miscellaneous do's and don'ts.

• Don't use floating-point variables where discrete values are needed. Using a float for a loop counter is a great way to shoot yourself in the foot. Always test floating-point numbers as <= or >=, never use an exact comparison (== or !=).

• Do not rely on automatic beautifiers. The main person who benefits from good program style is the programmer him/herself, and especially in the early design of handwritten algorithms or pseudo-code. Automatic beautifiers can only be applied to complete, syntactically correct programs and hence are not available when the need for attention to white space and indentation is greatest. Programmers can do a better job of making clear the complete visual layout of a function or file, with the normal attention to detail of a careful programmer (in other words, some of the visual layout is dictated by intent rather than syntax and beautifiers cannot read minds). Sloppy programmers should learn to be careful programmers instead of relying on a beautifier to make their code readable. Finally, since beautifiers are non-trivial programs that must parse the source, a sophisticated beautifier is not worth the benefits gained by such a program. Beautifiers are best for gross formatting of machine-generated code.

• Accidental omission of the second ``='' of the logical compare is a problem. The following is confusing and prone to error.

  
          if ($abool= $bbool) { ... }
       

  Does the programmer really mean assignment here? Often yes, but usually no. The solution is to just not do it, an inverse Nike philosophy. Instead use explicit tests and avoid assignment with an implicit test. The recommended form is to do the assignment before doing the test:

  
         $abool= $bbool;
         if ($abool) { ... }
      

Use if (0) to Comment Out Code Blocks

Sometimes large blocks of code need to be commented out for testing. The easiest way to do this is with an if (0) block:

   function example()
   {
      great looking code

      if (0) {
      lots of code
      }

      more code
    }

You can't use /**/ style comments because comments can't contain comments and surely a large block of your code will contain a comment, won't it?

Different Accessor Styles

Implementing Accessors

There are two major idioms for creating accessors.

Get/Set

   class X
   {
      function GetAge()        { return $this->mAge; }
      function SetAge($age)    { $this->mAge = $age; }
      var $mAge;
   };

Get/Set is ugly. Get and Set are strewn throughout the code cluttering it up.

But one benefit is when used with messages the set method can transparently transform from native machine representations to network byte order.

Attributes as Objects

   class X
   {
      function         Age()          { return $this->mAge; }
      function         Name()         { return $this->mName; }

      var              $mAge;
      var              $mName;
   }

   $x = new X;

   // Example 1
   $age = $x->Age();
   $r_age = &$x->Age(); // Reference

   // Example 2
   $name = $x->Name();
   $r_name = &$x->Name(); // Reference

Attributes as Objects is clean from a name perspective. When possible use this approach to attribute access.

Layering

Layering is the primary technique for reducing complexity in a system. A system should be divided into layers. Layers should communicate between adjacent layers using well defined interfaces. When a layer uses a non-adjacent layer then a layering violation has occurred.

A layering violation simply means we have dependency between layers that is not controlled by a well defined interface. When one of the layers changes code could break. We don't want code to break so we want layers to work only with other adjacent layers.

Sometimes we need to jump layers for performance reasons. This is fine, but we should know we are doing it and document appropriately.

Code Reviews

If you can make a formal code review work then my hat is off to you. Code reviews can be very useful. Unfortunately they often degrade into nit picking sessions and endless arguments about silly things. They also tend to take a lot of people's time for a questionable payback.

My god he's questioning code reviews, he's not an engineer!

Not really, it's the form of code reviews and how they fit into normally late chaotic projects is what is being questioned.

First, code reviews are way too late to do much of anything useful. What needs reviewing are requirements and design. This is where you will get more bang for the buck.

Get all relevant people in a room. Lock them in. Go over the class design and requirements until the former is good and the latter is being met. Having all the relevant people in the room makes this process a deep fruitful one as questions can be immediately answered and issues immediately explored. Usually only a couple of such meetings are necessary.

If the above process is done well coding will take care of itself. If you find problems in the code review the best you can usually do is a rewrite after someone has sunk a ton of time and effort into making the code "work."

You will still want to do a code review, just do it offline. Have a couple people you trust read the code in question and simply make comments to the programmer. Then the programmer and reviewers can discuss issues and work them out. Email and quick pointed discussions work well. This approach meets the goals and doesn't take the time of 6 people to do it.

Create a Source Code Control System Early and Not Often

A common build system and source code control system should be put in place as early as possible in a project's lifecycle, preferably before anyone starts coding. Source code control is the structural glue binding a project together. If programmers can't easily use each other's products then you'll never be able to make a good reproducible build and people will piss away a lot of time. It's also hell converting rogue build environments to a standard system. But it seems the right of passage for every project to build their own custom environment that never quite works right.

Some issues to keep in mind:

• Shared source environments like CVS usually work best in largish projects.
• If you use CVS use a reference tree approach. With this approach a master build tree is kept of various builds. Programmers checkout source against the build they are working on. They only checkout what they need because the make system uses the build for anything not found locally. Using the -I and -L flags makes this system easy to setup. Search locally for any files and libraries then search in the reference build. This approach saves on disk space and build time.
• Get a lot of disk space. With disk space as cheap it is there is no reason not to keep plenty of builds around.
• Make simple things simple. It should be dead simple and well documented on how to:
  • check out modules to build
  • how to change files
  • how to add new modules into the system
  • how to delete modules and files
  • how to check in changes
  • what are the available libraries and include files
  • how to get the build environment including all compilers and other tools

  Make a web page or document or whatever. New programmers shouldn't have to go around begging for build secrets from the old timers.

• On checkins log comments should be useful. These comments should be collected every night and sent to interested parties.

Sources

If you have the money many projects have found Clear Case a good system. Perfectly workable systems have been built on top of GNU make and CVS. CVS is a freeware build environment built on top of RCS. Its main difference from RCS is that is supports a shared file model to building software.

Create a Bug Tracking System Early and Not Often

The earlier people get used to using a bug tracking system the better. If you are 3/4 through a project and then install a bug tracking system it won't be used. You need to install a bug tracking system early so people will use it.

Programmers generally resist bug tracking, yet when used correctly it can really help a project:

• Problems aren't dropped on the floor.
• Problems are automatically routed to responsible individuals.
• The lifecycle of a problem is tracked so people can argue back and forth with good information.
• Managers can make the big schedule and staffing decisions based on the number of and types of bugs in the system.
• Configuration management has a hope of matching patches back to the problems they fix.
• QA and technical support have a communication medium with developers.

Not sexy things, just good solid project improvements.

Source code control should be linked to the bug tracking system. During the part of a project where source is frozen before a release only checkins accompanied by a valid bug ID should be accepted. And when code is changed to fix a bug the bug ID should be included in the checkin comments.

Sources

You can try AllTasks.net for bug tracking.

Honor Responsibilities

Responsibility for software modules is scoped. Modules are either the responsibility of a particular person or are common. Honor this division of responsibility. Don't go changing things that aren't your responsibility to change. Only mistakes and hard feelings will result.

Face it, if you don't own a piece of code you can't possibly be in a position to change it. There's too much context. Assumptions seemingly reasonable to you may be totally wrong. If you need a change simply ask the responsible person to change it. Or ask them if it is OK to make such-n-such a change. If they say OK then go ahead, otherwise holster your editor.

Every rule has exceptions. If it's 3 in the morning and you need to make a change to make a deliverable then you have to do it. If someone is on vacation and no one has been assigned their module then you have to do it. If you make changes in other people's code try and use the same style they have adopted.

Programmers need to mark with comments code that is particularly sensitive to change. If code in one area requires changes to code in an another area then say so. If changing data formats will cause conflicts with persistent stores or remote message sending then say so. If you are trying to minimize memory usage or achieve some other end then say so. Not everyone is as brilliant as you.

The worst sin is to flit through the system changing bits of code to match your coding style. If someone isn't coding to the standards then ask them or ask your manager to ask them to code to the standards. Use common courtesy.

Code with common responsibility should be treated with care. Resist making radical changes as the conflicts will be hard to resolve. Put comments in the file on how the file should be extended so everyone will follow the same rules. Try and use a common structure in all common files so people don't have to guess on where to find things and how to make changes. Checkin changes as soon as possible so conflicts don't build up.

As an aside, module responsibilities must also be assigned for bug tracking purposes.

PHP Code Tags

PHP Tags are used for delimit PHP from html in a file. There are serval ways to do this. <?php ?>, <? ?>, <script language="php"> </script>, <% %>, and <?=$name?>. Some of these may be turned off in your PHP settings.

• Use <?php ?>

Justification

• <?php ?> is always avaliable in any system and setup.

Example

<?php print "Hello world"; ?> // Will print "Hello world"

<?php print "Hello world"; ?> // Will print "Hello world"

<script language="php"> print "Hello world"; </script> // Will print "Hello world"

<% print "Hello world"; %> // Will print "Hello world"

<?=$street?> // Will print the value of the variable $street

No Magic Numbers

A magic number is a bare-naked number used in source code. It's magic because no-one has a clue what it means including the author inside 3 months. For example:

if      (22 == $foo) { start_thermo_nuclear_war(); }
else if (19 == $foo) { refund_lotso_money(); }
else if (16 == $foo) { infinite_loop(); }
else                 { cry_cause_im_lost(); }

In the above example what do 22 and 19 mean? If there was a number change or the numbers were just plain wrong how would you know?

Heavy use of magic numbers marks a programmer as an amateur more than anything else. Such a programmer has never worked in a team environment or has had to maintain code or they would never do such a thing.

Instead of magic numbers use a real name that means something. You should use define(). For example:

define("PRESIDENT_WENT_CRAZY", "22");
define("WE_GOOFED", "19");
define("THEY_DIDNT_PAY", "16");

if      (PRESIDENT_WENT_CRAZY == $foo) { start_thermo_nuclear_war(); }
else if (WE_GOOFED            == $foo) { refund_lotso_money(); }
else if (THEY_DIDNT_PAY       == $foo) { infinite_loop(); }
else                                   { happy_days_i_know_why_im_here(); }

Now isn't that better?

Thin vs. Fat Class Interfaces

How many methods should an object have? The right answer of course is just the right amount, we'll call this the Goldilocks level. But what is the Goldilocks level? It doesn't exist. You need to make the right judgment for your situation, which is really what programmers are for :-)

The two extremes are thin classes versus thick classes. Thin classes are minimalist classes. Thin classes have as few methods as possible. The expectation is users will derive their own class from the thin class adding any needed methods.

While thin classes may seem "clean" they really aren't. You can't do much with a thin class. Its main purpose is setting up a type. Since thin classes have so little functionality many programmers in a project will create derived classes with everyone adding basically the same methods. This leads to code duplication and maintenance problems which is part of the reason we use objects in the first place. The obvious solution is to push methods up to the base class. Push enough methods up to the base class and you get thick classes.

Thick classes have a lot of methods. If you can think of it a thick class will have it. Why is this a problem? It may not be. If the methods are directly related to the class then there's no real problem with the class containing them. The problem is people get lazy and start adding methods to a class that are related to the class in some willow wispy way, but would be better factored out into another class. Judgment comes into play again.

Thick classes have other problems. As classes get larger they may become harder to understand. They also become harder to debug as interactions become less predictable. And when a method is changed that you don't use or care about your code will still have to be retested, and rereleased.

Recent Changes

1. 2003-02-17. Modified indent rule.
2. 2002-03-04. Some changes in PHP File Extensions section. Only .php extensions is now recommended.
3. 2002-01-23. I've added Array Element.
4. 2001-08-13. The Variable Names example is now compatible with this PHP standard. Added word version of this document submitted by Chris Hubbard.
5. 2001-01-23. Method Argument Names example code fix. Parts of Different Accessor Styles has been deprecated because there was no support in PHP for these.
6. 2000-12-12. HTTP_*_VARS added
7. 2000-12-11. Indentation/Tabs/Space Policy has been changed
   PHP Code Tags added
8. 2000-12-05. Method Argument Names has been updated