PHP Manual: declare

declare

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
    statement

The directive section allows the behavior of the declare block to be set. Currently only three directives are recognized:

As directives are handled as the file is being compiled, only literals may be given as directive values. Variables and constants cannot be used. To illustrate:

<?php
// This is valid:
declare(ticks=1);

// This is invalid:
const TICK_VALUE = 1;
declare(ticks=TICK_VALUE);
?>

The statement part of the declare block will be executed - how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it (however if the file with declare was included then it does not affect the parent file).

<?php
// these are the same:

// you can use this:
declare(ticks=1) {
    // entire script here
}

// or you can use this:
declare(ticks=1);
// entire script here
?>

Ticks

A tick is an event that occurs for every N low-level tickable statements executed by the parser within the declare block. The value for N is specified using ticks=N within the declare block's directive section.

Not all statements are tickable. Typically, condition expressions and argument expressions are not tickable.

The event(s) that occur on each tick are specified using the register_tick_function. See the example below for more details. Note that more than one event can occur for each tick.

Example #1 Tick usage example

<?php

declare(ticks=1);

// A function called on each tick event
function tick_handler()
{
    echo "tick_handler() called\n";
}

register_tick_function('tick_handler'); // causes a tick event

$a = 1; // causes a tick event

if ($a > 0) {
    $a += 2; // causes a tick event
    print $a; // causes a tick event
}

?>

See also register_tick_function and unregister_tick_function.

Encoding

A script's encoding can be specified per-script using the encoding directive.

Example #2 Declaring an encoding for the script

<?php
declare(encoding='ISO-8859-1');
// code here
?>

Caution

When combined with namespaces, the only legal syntax for declare is declare(encoding='...'); where ... is the encoding value. declare(encoding='...') {} will result in a parse error when combined with namespaces.