assert_options
With all the discussion of how to best to use assert, I thought I would put my two cents in. I feel that errors should be thrown for potential things that could go wrong in production like failed database connections, but asserts should be used for sanity checks that should never fire unless there is an actual bug in the code.
When writing difficult code I use asserts to check for hard to find mistakes like unexpected race conditions. Then I leave them on (but logging only of course) in production. My assert statements tend to be very computationally cheap. In fact generally my assert statements are as simple as checking the return value from boolean functions.
This means I generally end up with alot of code like the following:
<?php
$result = flock($file, LOCK_EX); assert('$result');
$result = ftruncate($file, 0); assert('$result');
$result = fclose($file); assert('$result');
?>
I recently realized that I could write the much cleaner:
<?php
flock($file, LOCK_EX) or assert(0);
ftruncate($file, 0) or assert(0);
fclose($file) or assert(0);
?>
Much cleaner. Of course the error message doesn't tell me anything about the failure like it does when you pass a string. But an assertion failing means I have a major bug in my code, so its not too much work to look up the line number and figure out the error.
Also note that I don't use this for every boolean statement, since sometimes a failure isn't cause for an error. For example when I create a new user in the database, if the query fails its not an error, it just means the username is taken. If I did an assert there it would have to check that the query was successful or the mysql_errno was what I anticipated. But I could do that as follows:
<?php
mysql_query("INSERT INTO users (username, password) VALUES ('{$username}','{$password}')") or assert('mysql_errno()===1061');
?>
assert
(PHP 4, PHP 5)
assert — Checks if assertion is FALSE
Description
assert() will check the given assertion and take appropriate action if its result is FALSE.
If the assertion is given as a string it will be evaluated as PHP code by assert(). The advantages of a string assertion are less overhead when assertion checking is off and messages containing the assertion expression when an assertion fails. This means that 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 the assert_options() function, 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)
Parameters
- assertion
-
The assertion.
Return Values
FALSE if the assertion is false, TRUE otherwise.
Examples
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("")');
?>
add a note
User Contributed Notesassert
stangelanda at gmail dot com
23-Jan-2008 05:24
23-Jan-2008 05:24
dexen + goofy _ pl
29-Nov-2007 11:19
29-Nov-2007 11:19
Summary: turn assert() checking in production site, and use plain conditionals coupled with error reporting (trigger_error() or throw) for check that must be performed always.
I'd like to support oppinion of Matthew (matthew, at teh dot ath dot cx), and oppose the one of Tom (tom russo at gmail dot com).
When developing a program, you clearly want to check for various conditions, for example input validity and conformance of results of computation to various constraints, like database format. However, while some of the checks are mandatory, because supplied data varies with every request, others aren't, for example result of computations. Well written function will behave reasonably for *any* input -- either compute result/perform action, or signal error, be it return value or exception. And if a function takes input from trusted source, like another function you wrote, you don't need to check for all possible problems.
This is important distinction -- while developing, your incomplete and/or buggy function may return invalid result. Or a wrong kind of argument may be passed to your function. Or the code may, in some corner case, generate suprious data. This is where assertion comes in hand, to detect such conditions, signal to developer, and possibly stop execution, to prevent data loss.
However, the assumption is, that you ship code not earlier than the functions are complete. This means, you should not need checking of such conditions. If your code is incomplete, you don't ship, simple as that. Or label it as test version.
For checks that are required for every execution of code, you want plain IFs, is_* functions and so on, coupled with trigger_error() and/or throw statement. Wrapping assertions around those will not help it at all, even slightly impact performance. There simply is no point in using assert() there. You can get as detailed error reports with throw and exception handlers or with trigger_error() as with assert().
On the other hand, for checks that are needed only during development, you use assert(' condition ' ), since it can be turned off, and no performance impact occurs.
There is also a catch: error report form assert() may be verbose enough to reveal confidential data. What if you forget to turn assertion checking off and one is triggered in database connection setup code, with stack backtrace revealing DB username and password?
Krzysztof 'ChanibaL' Bociurko
02-Oct-2007 03:13
02-Oct-2007 03:13
Note that func_get_args() should be used carefully and never in a string! For example:
<?php
function asserted_normal($a, $b) {
assert(var_dump(func_get_args()));
}
function asserted_string($a, $b) {
assert('var_dump(func_get_args())');
}
?>
<?php asserted_normal(1,2) ?> prints
array(2) {
[0]=>
int(1)
[1]=>
int(2)
}
but <?php asserted_string(3,4) ?> prints
array(1) {
[0]=>
string(25) "var_dump(func_get_args())"
}
This is because of that the string passed to assert() is being evaled inside assert, and not your function. Also, note that this works correctly, because of the eval scope:
<?php
function asserted_evaled_string($a, $b) {
assert(eval('var_dump(func_get_args())'));
}
asserted_evaled_string(5,6);
?>
array(2) {
[0]=>
int(5)
[1]=>
int(6)
}
(oh, and for simplicity's sake the evaled code doesn't return true, so don't worry that it fails assertion...)
matthew, at teh dot ath dot cx
16-Sep-2007 05:15
16-Sep-2007 05:15
Much of the value of assertions comes from the assumption that you can do performance intensive checking for debugging that will not affect the code in production. Breaking the assumption that assertions will not be routinely enabled in production prohibits this usage and is counterproductive.
tom russo at gmail dot com
25-Dec-2006 12:25
25-Dec-2006 12:25
hodgman at ali dot com dot au said:
"Assertions should only be enabled during testing/development, and then disabled once your code reaches a production stage."
Assertions should _not_ be turned off in production code. Although it's common to do so, turning off assertions in production is a bad practice.
If your production code fails an assert, YOU WANT TO KNOW ABOUT IT. Asserts are a debugging tool, but you should not stop debugging your code just because it has gone into production.
Many people claim that removing asserts gives a performance benefit. In modern programming languages this simply isn't true. If you were doing an assert on something that is extremely slow/expensive to compute, you might consider turning that assert off. But in practice this really isn't how asserts are used.
There's a good discussion of this issue in the book The Pragmatic Programmer.
mail<at>aaron-mueller.de
13-Sep-2006 07:51
13-Sep-2006 07:51
Here is a simple demonstration of Design By Contract with PHP
<?php
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_BAIL, 1);
assert_options(ASSERT_CALLBACK, 'dcb_callback');
function dcb_callback($script, $line, $message) {
echo "<h1>Condition failed!</h1><br />
Script: <strong>$script</strong><br />
Line: <strong>$line</strong><br />
Condition: <br /><pre>$message</pre>";
}
// Parameters
$a = 5;
$b = 'Simple DCB with PHP';
// Pre-Condition
assert('
is_integer($a) &&
($a > 0) &&
($a < 20) &&
is_string($b) &&
(strlen($b) > 5);
');
// Function
function combine($a, $b) {
return "Kombined: " . $b . $a;
}
$result = combine($a, $b);
// Post-Condition
assert('
is_string($result) &&
(strlen($result) > 0);
');
// All right, the Function works fine
var_dump($result);
?>
hodgman at ali dot com dot au
11-Aug-2006 01:45
11-Aug-2006 01:45
I dont agree with gk at proliberty dot com's statements below.
If you are constantly enabling assertions before each assertion, then you are removing the functionality provided by being able to turn off assertions in the first place.
Assertions should only be enabled during testing/development, and then disabled once your code reaches a production stage.
This means you should either leave disabling/enabling assertions up to the INI file, or let the entry point of the script decide.
If you need an assertion to be there in the final copy of the code, then you are using the wrong tool. Assertions are a tool for debugging only.
gk at proliberty dot com
27-Aug-2005 04:35
27-Aug-2005 04:35
If you expect your code to be able to work well with other code, then you should not make any assumptions about the current state of assert_options() flags, prior to calling assert(): other code may disable ASSERT_ACTIVE, without you knowing it - this would render assert() useless!
To avoid this, ALWAYS set assert_options() IMMEDIATELY before calling assert(), per the C++ paradigm for assertion usage:
In one C++ source file, you can define and undefine NDEBUG multiple times, each time followed by #include <cassert>, to enable or disable the assert macro multiple times in the same source file.
Here is how I workaround this issue in my PHP code:
//////////////////////////////////////////////////////////////////////
/// phpxAssertHandler_f
//////////////////////////////////////////////////////////////////////
/**
* @desc Handler which also sets up assert options if not being called as handler
Always fatal when assertion fails
Always make sure assertion is enabled
Cannot depend on other code not using assert or using its own assert handler!
USAGE:
// customize error level of assertion (php assert_options() only allows E_WARNING or nothing at all):
phpxAssertHandler_f(E_USER_NOTICE);
// control assertion active state: not dependent on anything another piece of code might do with ASSERT_ACTIVE
$GLOBALS['MY_ASSERT_ACTIVE']=false;
phpxAssertHandler_f(E_USER_NOTICE,$GLOBALS['MY_ASSERT_ACTIVE']);
// use alternate assertion callback function:
// NOTE: pass null as custom options parameter to use default options
// NOTE: pass no values for assert options parameter array elements to use default options
$GLOBALS['MY_ASSERT_ACTIVE']=false;
$GLOBALS['MY_ASSERT_CALLBACK']='myAssertCallback';
phpxAssertHandler_f(
null,
array(
0=>$GLOBALS['MY_ASSERT_ACTIVE'],
3=>$GLOBALS['MY_ASSERT_CALLBACK'],
)
);
* @param mixed = file or options
* @param line
* @param code
* @return void
*/
function phpxAssertHandler_f($file_or_custom_options=null, $line_or_assert_options=null, $code=null){
static $custom_options;
$debug = false;
if (is_null($code)){
// set default assert_options
$assert_options[]=1;//ASSERT_ACTIVE
$assert_options[]=0;//ASSERT_WARNING -
$assert_options[]=0;//ASSERT_QUIET_EVAL
$assert_options[]=__FUNCTION__;//ASSERT_CALLBACK
// set default custom_options
$custom_options[]=E_USER_ERROR;// error level
if (!is_null($line_or_assert_options)){
// assert_options are passed in
if (!is_array($line_or_assert_options)){
$line_or_assert_options=array($line_or_assert_options);
}
foreach ($line_or_assert_options as $i=>$assert_option){
if ($assert_option===true) $assert_option=1;
if ($assert_option===false) $assert_option=0;
$assert_options[$i]=$assert_option;
if($debug) echo ("assert_options[$i]=$assert_option\n");
}
}
if (!is_null($file_or_custom_options)){
// custom_options are passed in
if (!is_array($file_or_custom_options)){
$file_or_custom_options=array($file_or_custom_options);
}
foreach ($file_or_custom_options as $i=>$custom_option){
if ($custom_option===true) $custom_option=1;
if ($custom_option===false) $custom_option=0;
$custom_options[$i]=$custom_option;
if($debug) echo ("custom_options[$i]=$custom_option\n");
}
}
// set assert options
@assert_options (ASSERT_ACTIVE, $assert_options[0]);
@assert_options (ASSERT_WARNING, $assert_options[1]);
@assert_options (ASSERT_QUIET_EVAL, $assert_options[2]);
@assert_options (ASSERT_CALLBACK, $assert_options[3]);
} else {
// we are acting as a callback function
$file = $file_or_custom_options;
$line = $line_or_assert_options;
$msg="ASSERTION FAILED: $code";
phpxErrorHandler_f ($custom_options[0],$msg,$file,$line);
}
}//phpxAssertHandler_f()
Thomas
28-Mar-2005 05:56
28-Mar-2005 05:56
Another very good unit testing framework is SimpleTest, which can be found at http://www.lastcraft.com/simple_test.php
It has very good documentation, support for mock objects and tools for automating testing of entire web sites.
nyk at forumone dot com
27-Aug-2002 03:56
27-Aug-2002 03:56
Assertion is a useful debugging feature, but for building unit tests and automated regression tests you should seriously consider using the PHPtest in the PEAR archive (http://pear.php.net/package-info.php?pacid=38) that is based on the JUnit framework for Java. There is also another unit testing framework, also based on JUnit and also called PHPunit on SourceForge (http://sourceforge.net/projects/phpunit/). I believe it is an independent effort from that on PEAR.