assert
(PHP 4, PHP 5, PHP 7, PHP 8)
assert — Checks if assertion is false
Description
PHP 5 and 7
PHP 7
assert() will check the given
assertion and take appropriate action if
its result is false.
Traditional assertions (PHP 5 and 7)
If the assertion is given as a string it
will be evaluated as PHP code by assert().
If you pass a boolean condition as assertion,
this condition will not show up as parameter to the assertion function
which you may have defined with assert_options().
The condition is converted to a string before calling that handler
function, and the boolean false is converted as the empty string.
Assertions should be used as a debugging feature only. You may
use them for sanity-checks that test for conditions that should
always be true and that indicate some programming errors if not
or to check for the presence of certain features like extension
functions or certain system limits and features.
Assertions should not be used for normal runtime operations like input parameter checks. As a rule of thumb your code should always be able to work correctly if assertion checking is not activated.
The behavior of assert() may be configured by assert_options() or by .ini-settings described in that functions manual page.
The assert_options() function and/or
ASSERT_CALLBACK configuration directive allow a
callback function to be set to handle failed assertions.
assert() callbacks are particularly useful for building automated test suites because they allow you to easily capture the code passed to the assertion, along with information on where the assertion was made. While this information can be captured via other methods, using assertions makes it much faster and easier!
The callback function should accept three arguments. The first
argument will contain the file the assertion failed in. The
second argument will contain the line the assertion failed on and
the third argument will contain the expression that failed (if
any — literal values such as 1 or "two" will not be passed via
this argument). Users of PHP 5.4.8 and later may also provide a fourth
optional argument, which will contain the
description given to assert(), if
it was set.
Expectations (PHP 7 only)
assert() is a language construct in PHP 7, allowing for the definition of expectations: assertions that take effect in development and testing environments, but are optimised away to have zero cost in production.
While assert_options() can still be used to control behaviour as described above for backward compatibility reasons, PHP 7 only code should use the two new configuration directives to control the behaviour of assert() and not call assert_options().
| Directive | Default value | Possible values |
|---|---|---|
| zend.assertions | 1 |
|
| assert.exception | 0 |
|
Parameters
-
assertion -
The assertion. In PHP 5, this must be either a string to be evaluated or a bool to be tested. In PHP 7, this may also be any expression that returns a value, which will be executed and the result used to indicate whether the assertion succeeded or failed.
WarningUsing string as the
assertionis DEPRECATED as of PHP 7.2.0 and REMOVED as of PHP 8.0.0. -
description -
An optional description that will be included in the failure message if the
assertionfails. From PHP 7, if no description is provided, a default description equal to the source code for the invocation of assert() is provided. -
exception -
In PHP 7, the second parameter can be a Throwable object instead of a descriptive string, in which case this is the object that will be thrown if the assertion fails and the assert.exception configuration directive is enabled.
Return Values
false if the assertion is false, true otherwise.
Changelog
| Version | Description |
|---|---|
| 8.0.0 |
assert() will no longer evaluate string arguments, instead they will be
treated like any other argument. assert($a == $b) should be used instead of
assert('$a == $b'). The assert.quiet_eval php.ini directive and
the ASSERT_QUIET_EVAL constant have also been removed, as they would no longer
have any effect.
|
| 8.0.0 |
Declaring a function called assert() inside a namespace is
no longer allowed, and issues E_COMPILE_ERROR.
|
| 7.3.0 |
Declaring a function called assert() inside a namespace
became deprecated. Such declaration now emits an E_DEPRECATED.
|
| 7.2.0 |
Usage of a string as the assertion
became deprecated. It now emits an E_DEPRECATED
notice when both assert.active
and zend.assertions are set
to 1.
|
| 7.0.0 |
assert() is now a language construct and not a
function. assertion can now be an expression.
The second parameter is now interpreted either as an
exception (if a
Throwable object is given), or as the
description supported from PHP 5.4.8 onwards.
|
Examples
Traditional assertions (PHP 5 and 7)
Example #1 Handle a failed assertion with a custom handler
<?php
// Active assert and make it quiet
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_QUIET_EVAL, 1);
// Create a handler function
function my_assert_handler($file, $line, $code)
{
echo "<hr>Assertion Failed:
File '$file'<br />
Line '$line'<br />
Code '$code'<br /><hr />";
}
// Set up the callback
assert_options(ASSERT_CALLBACK, 'my_assert_handler');
// Make an assertion that should fail
assert('mysql_query("")');
?>
Example #2 Using a custom handler to print a description
<?php
// Active assert and make it quiet
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_QUIET_EVAL, 1);
// Create a handler function
function my_assert_handler($file, $line, $code, $desc = null)
{
echo "Assertion failed at $file:$line: $code";
if ($desc) {
echo ": $desc";
}
echo "\n";
}
// Set up the callback
assert_options(ASSERT_CALLBACK, 'my_assert_handler');
// Make an assertion that should fail
assert('2 < 1');
assert('2 < 1', 'Two is less than one');
?>
The above example will output:
Assertion failed at test.php:21: 2 < 1 Assertion failed at test.php:22: 2 < 1: Two is less than one
Expectations (PHP 7 only)
Example #3 Expectations without a custom exception
<?php
assert(true == false);
echo 'Hi!';
?>
With zend.assertions set to 0, the above example will output:
Hi!
With zend.assertions set to 1 and assert.exception set to 0, the above example will output:
Warning: assert(): assert(true == false) failed in - on line 2 Hi!
With zend.assertions set to 1 and assert.exception set to 1, the above example will output:
Fatal error: Uncaught AssertionError: assert(true == false) in -:2 Stack trace: #0 -(2): assert(false, 'assert(true == ...') #1 thrown in - on line 2
Example #4 Expectations with a custom exception
<?php
class CustomError extends AssertionError {}
assert(true == false, new CustomError('True is not false!'));
echo 'Hi!';
?>
With zend.assertions set to 0, the above example will output:
Hi!
With zend.assertions set to 1 and assert.exception set to 0, the above example will output:
Warning: assert(): CustomError: True is not false! in -:4 Stack trace: #0 failed in - on line 4 Hi!
With zend.assertions set to 1 and assert.exception set to 1, the above example will output:
Fatal error: Uncaught CustomError: True is not false! in -:4 Stack trace: #0 thrown in - on line 4
