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• Status: Withdrawn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

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.

Adding parser support for compile-time resolved scalar expressions.

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.

• 123 - Integers
• 123.456 - Floats
• “foo” - Strings
• __LINE__ - Line magic constant
• __FILE__ - File magic constant
• __DIR__ - Directory magic constant
• __TRAIT__ - Trait magic constant
• __METHOD__ - Method magic constant
• __FUNCTION__ - Function magic constant
• __NAMESPACE__ - Namespace magic constant
• <<<HEREDOC - HEREDOC string syntax

constant_declarations.php

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

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.php

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

class_property_declarations.php

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

function_argument_declarations.php

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

static_variable_declarations.php

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

None

PHP 5.NEXT

None

None

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).

None

None

An implementation based off of current master is available: Implementation On GitHub (Diff On GitHub)

This patch is ready to be merged with tests.