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PHP implements a method to force the callback type to be specified based on Callable

Jun 01, 2018 pm 02:14 PM

callable php designation

This article mainly introduces the method of forcing PHP Callable to specify the callback type. It is very good and has reference value. Friends who need it can refer to it

If a method needs to accept a callback method as a parameter, we You can write like this

&lt;?php
function dosth($callback){
call_user_func($callback);
}
function callback(){
echo &#39;do sth callback&#39;;
}
dosth(&#39;callback&#39;);
?&gt;

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Output:

do sth callback

But we cannot be sure whether the callback method can be called, so A lot of extra work needs to be done to check whether this callback method can be called.

Is there any better way to determine whether the callback method is callable?
We can use callable to force the specified parameter to be a callback type, which ensures that the callback method must be callable.

For example, the callback method is a non-existent method

&lt;?php
function dosth(callable $callback){
call_user_func($callback);
}
dosth(&#39;abc&#39;);
?&gt;

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After execution, an error message is displayed: TypeError: Argument 1 passed to dosth() must be callable
The program cannot execute the internal processing of dosth. The parameter type has been checked and processed for protection.

And if the callable is removed

&lt;?php
function dosth($callback){
call_user_func($callback);
}
dosth(&#39;abc&#39;);
?&gt;

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After execution, a warning is displayed: Warning: call_user_func() expects parameter 1 to be a valid callback, function 'abc' not found or invalid function name

The program can execute the internal processing of dosth, so a lot of extra work needs to be done to check whether this callback method can be called.

Therefore, if the parameter of the method is a callback method, callable should be added to force it to be specified as the callback type. This can reduce calling errors and improve the quality of the program.

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study.

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