(PHP 4, PHP 5, PHP 7, PHP 8)
assert — Checks an assertion
assert() allows for the definition of expectations: assertions that take effect in development and testing environments, but are optimised away to have zero cost in production.
Assertions should be used as a debugging feature only.
One use case for them is to act as sanity-checks for preconditions
that should always be true and that if they aren't upheld this indicates
some programming errors.
Another use case is to ensure the presence of certain features like
extension functions or certain system limits and features.
As assertions can be configured to be eliminated, they should not be used for normal runtime operations like input parameter checks. As a rule of thumb code should behave as expected even if assertion checking is deactivated.
assert() will check that the expectation given in
assertion holds.
If not, and thus the result is false, it will take the appropriate action
depending on how assert() was configured.
The behaviour of assert() is dictated by the following INI settings:
| Name | Default | Description | Changelog |
|---|---|---|---|
| zend.assertions | 1 |
|
|
| assert.active | true |
If false, assert() does not check the expectation
and returns true, unconditionally.
|
Deprecated as of PHP 8.3.0. |
| assert.callback | null |
A user defined function to call when an assertion fails. It's signature should be: |
Prior to PHP 8.0.0, the signature of the callback should be: Deprecated as of PHP 8.3.0. |
| assert.exception | true |
If true will throw an AssertionError if the
expectation isn't upheld.
|
Deprecated as of PHP 8.3.0. |
| assert.bail | false |
If true will abort execution of the PHP script if the
expectation isn't upheld.
|
Deprecated as of PHP 8.3.0. |
| assert.warning | true |
If true, will emit an E_WARNING if the
expectation isn't upheld. This INI setting is ineffective if
assert.exception
is enabled.
|
Deprecated as of PHP 8.3.0. |
assertionThis is any expression that returns a value, which will be executed and the result is used to indicate whether the assertion succeeded or failed.
description
If description is an instance of
Throwable, it will be thrown only if the
assertion is executed and fails.
Note:
As of PHP 8.0.0, this is done prior to calling the potentially defined assertion callback.
Note:
As of PHP 8.0.0, the object will be thrown regardless of the configuration of assert.exception.
Note:
As of PHP 8.0.0, the assert.bail setting has no effect in this case.
If description is a string this message
will be used if an exception or a warning is emitted.
An optional description that will be included in the failure message if
the assertion fails.
If description is omitted.
A default description equal to the source code for the invocation of
assert() is created at compile time.
assert() will always return true if at least one of the following is true:
zend.assertions=0zend.assertions=-1assert.exception=1assert.bail=1description.
If none of the conditions are true assert() will return true if
assertion is truthy and false otherwise.
| Version | Description |
|---|---|
| 8.3.0 |
All assert. INI settings have been deprecated.
|
| 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 |
If description is an instance of
Throwable, the object is thrown if the assertion
fails, regardless of the value of
assert.exception.
|
| 8.0.0 |
If description is an instance of
Throwable, no user callback is called even
if it set.
|
| 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.
|
Example #1 assert() example
<?php
assert(1 > 2);
echo 'Hi!';
If assertions are enabled (zend.assertions=1)
the above example will output:
Fatal error: Uncaught AssertionError: assert(1 > 2) in example.php:2
Stack trace:
#0 example.php(2): assert(false, 'assert(1 > 2)')
#1 {main}
thrown in example.php on line 2
If assertions are disabled (zend.assertions=0 or zend.assertions=-1)
the above example will output:
Hi!
Example #2 Using a custom message
<?php
assert(1 > 2, "Expected one to be greater than two");
echo 'Hi!';If assertions are enabled the above example will output:
Fatal error: Uncaught AssertionError: Expected one to be greater than two in example.php:2
Stack trace:
#0 example.php(2): assert(false, 'Expected one to...')
#1 {main}
thrown in example.php on line 2
If assertions are disabled the above example will output:
Hi!
Example #3 Using a custom exception class
<?php
class ArithmeticAssertionError extends AssertionError {}
assert(1 > 2, new ArithmeticAssertionError("Expected one to be greater than two"));
echo 'Hi!';If assertions are enabled the above example will output:
Fatal error: Uncaught ArithmeticAssertionError: Expected one to be greater than two in example.php:4
Stack trace:
#0 {main}
thrown in example.php on line 4
If assertions are disabled the above example will output:
Hi!