declare
(PHP 4, PHP 5, PHP 7, PHP 8)
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: the
ticks directive (See below for more
information on the
ticks
directive), the encoding directive (See below for more
information on the
encoding
directive) and the strict_types directive (See for more
information the
strict typing
section on the type declarations page)
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
?>
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.
See also zend.script_encoding.
