Is there a way to do this in php?
//in a class
public static function myFunc($x = function($arg) { return 42+$arg; }) {
return $x(8); //return 50 if default func is passed in
}
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can I ask why you want to do it this way?tradyblix– tradyblix2012-10-11 03:24:47 +00:00Commented Oct 11, 2012 at 3:24
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well, I have a general utility function that takes anonymous function as an argument (specifically, it converts an assortment of objects into an assortment of arrays according to certain rules, which are performed by functions). I'd like to have a default action. Is that too much to ask? =xArcymag– Arcymag2012-10-11 03:26:22 +00:00Commented Oct 11, 2012 at 3:26
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No. Default parameters can only be constant values, not expressions, nor objects.mario– mario2012-10-11 03:34:51 +00:00Commented Oct 11, 2012 at 3:34
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2 Answers
PHP Default function arguments can only be of scalar or array types:
The default value must be a constant expression, not (for example) a variable, a class member or a function call.
From: PHP Manual / Function Arguments / Default argument values
How about:
public static function myFunc($x = null) {
if (null === $x) {
$x = function($arg) { return 42 + $arg; };
}
return $x(8); //return 50 if default func is passed in
}
2 Comments
Arcymag
answer accepted because of link to php manual which says "The default value must be a constant expression, not (for example) a variable, a class member or a function call." Thanks. I had something like this earlier, and I hoped there was a language feature for it. Guess not =(
Anthony
I would also advise declaring the type for
$x in the function signature since passing in a string would result in an error when $x(8) occurs. I personally would go with declaring the type as Closure to ensure it is an anonymous function, but callable would also work and be a bit more flexible (and error prone). So myFunc(Closure $x = null) or myFunc(callable $x = null), either one would throw a catchable fatal error if you tried myFunc("test"); versus a non-catchable fatal error if the type isn't declared.You can use func_num_args and func_get_arg
//in a class
public static function myFunc() {
if (func_num_args() >= 1) {
$x = func_get_arg(0);
} else {
$x = function($arg) { return 42+$arg; }
}
return $x(8); //return 50 if default func is passed in
}
But I agree with tradyblix that you could just process the data as in
//in a class
public static function myFunc() {
if (func_num_args() >= 1) {
$x = func_get_arg(0);
$retval = $x(8);
} else {
$retval = 42 + 8;
}
return $retval; //return 50 if default func is passed in
}
1 Comment
Arcymag
Didn't know about func_num_args and func_get_arg. How very bash.