PHP: Object of class Closure could not be converted to int - php

Question

I have a problem using the usort function. My array has the following model :
Fusion
|
| Array_1
| |
| | Array_1_1
| | | clock => "08:08"
| | | //Other fields
| | |
| |
| | Array_1_2
| | | clock => "04:51"
| | | //Other fields
| | |
|
| Array_2
| ...
I want to sort the arrays in Array_X basing on the 'clock' field. I made this code, basing on the PHP documentation of usort (4th example) :
foreach ($fusion as $fus){
usort($fus,function ($key = 'clock'){
return function ($a,$b) use ($key){
return strnatcmp($a[$key],$b[$key]);
};
});
}
... but it returns the following exception :
Object of class Closure could not be converted to int
Do you have any idea ? Thanks for your help.

Answer 1

You're trying to pass the following as a callback (2nd argument of usort)
function ($key = 'clock'){
return function ($a,$b) use ($key){
return strnatcmp($a[$key],$b[$key]);
};
}
But the documentation clearly specifies that
The comparison function must return an integer [...]
However, your callback returns another closure. This is why you get a Closure to int convertion Exception.
I believe what you're trying to do is to execute the inner-closure to get the final callback using the right values. I'd say this is useless because, unlike in Javascript, php closures are opt-in, not all-in, which means their context must be included with use the way you did for $key in the outer-closure.
You could simply do:
$key = 'clock';
foreach ($fusion as $fus){
usort($fus,function ($a,$b) use ($key){
return strnatcmp($a[$key],$b[$key]);
});
}
And if $key comes from some other kind of context you may just have to adjust the variable assignment.

Answer 2

Convert your object into an array using get_object_vars($object) first.
If the object that you are getting is generated by a different function, then read documentation for that function and find a way for it to return an array instead of object.
Examples and documentation can be found here http://php.net/manual/en/function.get-object-vars.php