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PHP assert

PHP original manual for assert [ show | php.net ]

assert

(PHP 4, PHP 5, PHP 7)

assert — Checks if assertion is FALSE

Description

PHP 5 and 7

bool assert ( mixed $assertion [, string $description ] )

PHP 7

bool assert ( mixed $assertion [, Throwable $exception ] )

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().

PHP 7 configuration directives for assert()
Directive Default value Possible values
zend.assertions 1
  • 1: generate and execute code (development mode)
  • 0: generate code but jump around it at runtime
  • -1: do not generate code (production mode)
assert.exception 0
  • 1: throw when the assertion fails, either by throwing the object provided as the exception or by throwing a new AssertionError object if exception wasn't provided
  • 0: use or generate a Throwable as described above, but only generate a warning based on that object rather than throwing it (compatible with PHP 5 behaviour)

Parameters

assertion

The assertion. In PHP 5, this must be either a string to be evaluated or a boolean 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.

Warning

Using string as the assertion is DEPRECATED as of PHP 7.2.

description

An optional description that will be included in the failure message if the assertion fails.

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
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.
5.4.8 The description parameter was added. The description is also now provided to a callback function in ASSERT_CALLBACK mode as the fourth argument.

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 {main}
  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 {main} 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 {main}
  thrown in - on line 4

See Also