====== PHP RFC: Constant Scalar Expressions ======
  * Version: 1.0
  * Date: 2013-08-13
  * Author: Anthony Ferrara <ircmaxell@php.net>
  * Status: Withdrawn
  * First Published at: http://wiki.php.net/rfc/const_scalar_expressions

===== Introduction =====

This RFC brings static scalar expressions to the parser. This allows places that only take static values (const declarations, property declarations, function arguments, etc) to also be able to take static expressions.

This can allow for writing far easier to understand code, by allowing for far more expressive code. 

===== Proposal =====

Adding parser support for compile-time resolved scalar expressions. 

==== Supported Operations ====

The following operations are currently supported by this proposal:

  * //+// - Addition
  * //-// - Subtraction
  * //*// - Multiplication
  * ///// - Division
  * //%// - Modulus
  * //!// - Boolean Negation
  * //~// - Bitwise Negation
  * //|// - Bitwise OR
  * //&// - Bitwise AND
  * //^// - Bitwise XOR
  * //<<// - Bitwise Shift Left
  * //>>// - Bitwise Shift Right
  * //.// - Concat

Also supported is grouping static operations: //(1 + 2) + 3//.

==== Supported Operands ====

  * //123// - Integers
  * //123.456// - Floats
  * //"foo"// - Strings
  * //<nowiki>__LINE__</nowiki>// - Line magic constant
  * //<nowiki>__FILE__</nowiki>// - File magic constant
  * //<nowiki>__DIR__</nowiki>// - Directory magic constant
  * //<nowiki>__TRAIT__</nowiki>// - Trait magic constant
  * //<nowiki>__METHOD__</nowiki>// - Method magic constant
  * //<nowiki>__FUNCTION__</nowiki>// - Function magic constant
  * //<nowiki>__NAMESPACE__</nowiki>// - Namespace magic constant
  * //<nowiki><<<HEREDOC</nowiki>// - HEREDOC string syntax

==== Constant Declarations ====

<file php constant_declarations.php>
<?php
const FOO = 1 + 1;
const BAR = 1 << 1;
const BAZ = "HELLO " . "WORLD!";
?>
</file>

Note that constants are not supported within a declaration (since this happens at compile time). So //const BIZ = FOO << BAR;// would be a compile error.

==== Class Constant Declarations ====

<file php class_constant_declarations.php>
<?php
class Foo {
    const FOO = 1 + 1;
    const BAR = 1 << 1;
    const BAZ = "HELLO " . "WORLD!";
}
?>
</file>

==== Class Property Declarations ====

<file php class_property_declarations.php>
<?php
class Foo {
    public $foo = 1 + 1;
    public $bar = [
        1 + 1,
        1 << 2,
        "foo " . 
            "bar"
    ];
    public $baseDir = __DIR__ . "/base";
}
?>
</file>

==== Function Argument Declarations ====

<file php function_argument_declarations.php>
<?php
function foo($a = 1 + 1, $b = 2 << 3) {
}
?>
</file>

==== Static Variable Declarations ====

<file php static_variable_declarations.php>
<?php
function foo() {
    static $a = 1 + 1 
    static $b = [ 1 << 2 ];    
}
?>
</file>

===== Backward Incompatible Changes =====

None

===== Proposed PHP Version(s) =====

PHP 5.NEXT

===== SAPIs Impacted =====

None

===== Impact to Existing Extensions =====

None

===== Impact to Opcode Caching =====

None, as this is a pure compile-time construct, the generated op-array is the same as if there was no expression (it's purely static).

===== New Constants =====

None

===== php.ini Defaults =====

None

===== Patches and Tests =====

An implementation based off of current master is available: [[https://github.com/ircmaxell/php-src/tree/static_operation_parsing|Implementation On GitHub]] ([[https://github.com/ircmaxell/php-src/compare/static_operation_parsing|Diff On GitHub]])

This patch is ready to be merged with tests.