[PHP] Assignment in Conditional - How are they evaluated?
How is the following evaluated: [code] if ($data = somefunc()) ... [/code] Ignoring the 'assignment inside condition' arguments, is the return value of somefunc() assigned to $data, and then $data's value is evaluated (to true or false), or is the actual assignment tested (does the assignment fail, etc)? -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Assignment in Conditional - How are they evaluated?
On Thu, 2009-10-29 at 13:58 +, Mark Skilbeck wrote: How is the following evaluated: [code] if ($data = somefunc()) ... [/code] Ignoring the 'assignment inside condition' arguments, is the return value of somefunc() assigned to $data, and then $data's value is evaluated (to true or false), or is the actual assignment tested (does the assignment fail, etc)? I believe that it determines if the return value of somefunc() is non-false. It will have the added benefit then that you can use the return value afterwards if it was, for example, not true, but a string or something instead. Thanks, Ash http://www.ashleysheridan.co.uk
Re: [PHP] Assignment in Conditional - How are they evaluated?
On Thu, Oct 29, 2009 at 10:58 AM, Mark Skilbeck markskilb...@gmail.comwrote: How is the following evaluated: [code] if ($data = somefunc()) ... [/code] Ignoring the 'assignment inside condition' arguments, is the return value of somefunc() assigned to $data, and then $data's value is evaluated (to true or false), or is the actual assignment tested (does the assignment fail, etc)? -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php The code is interpreted this way... $data = somefunc(); if ($data) -- Martin Scotta
Re: [PHP] Assignment in Conditional - How are they evaluated?
Ashley Sheridan wrote:
On Thu, 2009-10-29 at 13:58 +, Mark Skilbeck wrote:
How is the following evaluated:
[code]
if ($data = somefunc()) ...
[/code]
Ignoring the 'assignment inside condition' arguments, is the return
value of somefunc() assigned to $data, and then $data's value is
evaluated (to true or false), or is the actual assignment tested (does
the assignment fail, etc)?
I believe that it determines if the return value of somefunc() is
non-false. It will have the added benefit then that you can use the
return value afterwards if it was, for example, not true, but a string
or something instead.
I do this all the time... an example is the following:
?php
if( ($user = get_current_user()) )
{
// Yay, we have a user... do something.
echo $user-name();
}
else
{
// Handle no current user.
echo 'Anonymous';
}
?
Cheers,
Rob.
--
http://www.interjinn.com
Application and Templating Framework for PHP
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Fwd: [PHP] Assignment in Conditional - How are they evaluated?
On Thu, Oct 29, 2009 at 11:11 AM, Robert Cummings rob...@interjinn.comwrote:
Ashley Sheridan wrote:
On Thu, 2009-10-29 at 13:58 +, Mark Skilbeck wrote:
How is the following evaluated:
[code]
if ($data = somefunc()) ...
[/code]
Ignoring the 'assignment inside condition' arguments, is the return value
of somefunc() assigned to $data, and then $data's value is evaluated (to
true or false), or is the actual assignment tested (does the assignment
fail, etc)?
I believe that it determines if the return value of somefunc() is
non-false. It will have the added benefit then that you can use the
return value afterwards if it was, for example, not true, but a string
or something instead.
I do this all the time... an example is the following:
?php
if( ($user = get_current_user()) )
{
// Yay, we have a user... do something.
echo $user-name();
}
else
{
// Handle no current user.
echo 'Anonymous';
}
?
Cheers,
Rob.
--
http://www.interjinn.com
Application and Templating Framework for PHP
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
There is a situation when common-sense can fail...
if( $a $b = do_something() )
The problem here is the precedence between and =
The correct sentence will be...
if( $a ($b = do_something()) )
C coders knows this behaviour very well.
cheers,
Martin Scotta
--
Martin Scotta
Re: [PHP] Assignment in Conditional - How are they evaluated?
On Thu, Oct 29, 2009 at 10:23 AM, Martin Scotta martinsco...@gmail.com wrote:
On Thu, Oct 29, 2009 at 11:11 AM, Robert Cummings rob...@interjinn.comwrote:
Ashley Sheridan wrote:
On Thu, 2009-10-29 at 13:58 +, Mark Skilbeck wrote:
How is the following evaluated:
[code]
if ($data = somefunc()) ...
[/code]
Ignoring the 'assignment inside condition' arguments, is the return value
of somefunc() assigned to $data, and then $data's value is evaluated (to
true or false), or is the actual assignment tested (does the assignment
fail, etc)?
I believe that it determines if the return value of somefunc() is
non-false. It will have the added benefit then that you can use the
return value afterwards if it was, for example, not true, but a string
or something instead.
I do this all the time... an example is the following:
?php
if( ($user = get_current_user()) )
{
// Yay, we have a user... do something.
echo $user-name();
}
else
{
// Handle no current user.
echo 'Anonymous';
}
?
Cheers,
Rob.
--
http://www.interjinn.com
Application and Templating Framework for PHP
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
There is a situation when common-sense can fail...
if( $a $b = do_something() )
The problem here is the precedence between and =
The correct sentence will be...
if( $a ($b = do_something()) )
C coders knows this behaviour very well.
cheers,
Martin Scotta
--
Martin Scotta
Assignment operations in PHP have the side effect of returning the
assignment. For example:
function return_false() {
return false;
}
var_dump(return_false()); //bool(false);
var_dump($a = return_false()); //bool(false);
var_dump($a = 1); // int(1)
var_dump($a = hello world!); //string...
So the same thing that allows you to do:
$a = $b = $c = $d = 154;
which works because $d = 154 returns 154, which is assigned to $c,
which returns 154... is how assignment in conditionals or looping
works:
if($a = return_false()) { }
var_dump($a); //bool(false)
if($a = hello) {}
var_dump($a); //string, hello
So what's really happening is the return value of the expression $a =
is evaluated and that's used to determine the truth of the
conditionality. if($a = return_false()) is exactly the same thing as
if(return_false()) save for you capture the output of the function,
rather than just allow the conditional operator to see it. It's
functionally equivalent to $a = return_false(); if($a) {} but it's
important to understand that __assigning a variable to a value in PHP
is an expression with a return value___ and that return value is the
value that you assigned to the variable.
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