dongzha0813 2017-03-13 13:27
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从closure返回一个值到main方法

I have a closure as follows:

public function create(){
   DB::transaction(function(){
       return 'function called'
   });

how can I return "function called" from create?

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  • douan4106 2017-03-13 14:34
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    this is depends on the implementation of the closure ,

    take this quick example:

    function transaction($inReturnable, $returnable)
    {
        $inReturnable();
    
        return $returnable();
    }
    
    $value = transaction(function() {
        return 'hello!';
    }, function() {
        return 'yello!';
    });
    
    echo $value;
    // Output: yello!
    

    so, how this could be useful ?

    -- some time you want give the client user of your object the power to use some of your object methods or properties without any effect on your object context, you need your method to return something else , in the same time that you need to give the user access to do something within your object/method, it's a kind of dependency injection so to speak .

    function transaction($inReturnable, $returnable)
    {
        $privateVariable = 'Hello';
        $inReturnable($privateVariable);
    
        return $returnable();
    }
    
    $value = transaction(function($privateVariable) {
        echo $privateVariable . "
    ";
    }, function() {
        echo $privateVariable; // Notice: Undefined variable: privateVariable
        return 'yello!';
    });
    
    echo $value;
    // Output: Hello 
    Notice: Undefined variable: privateVariable
    yello!
    

    live example for this kind of implementing, the difference between array_map and array_walk internal functions in php

    array_walk :

    Returns TRUE on success or FALSE on failure.

    array_map :

    Returns an array containing all the elements of array1 after applying the callback function to each one.

    it's kind of : the following is just a pseudo-code

    // imagined implementation of array_map
    array function array_map(callable $callback, array $array)
    {
        return $callback if true;
    }
    
    // imagined implementation of array_walk
    array function array_walk(array $array, callable $callback)
    {
        return true if true;
    }
    

    for example:

    $array = [1,2,3];
    
    $map = array_map(function($value) {return $value * 3;}, $array);
    
    print_r($map);
    
    $walk = array_walk($array, function($value, $key) {return $value * 3;});
    
    // will return true
    print_r($walk);
    
    array_walk($array, function($value, $key) use (&$array) {return $array[$key] = $value * 3;});
    
    print_r($array);
    

    this will output:

    Array ( [0] => 3 [1] => 6 [2] => 9 )
    1
    Array ( [0] => 3 [1] => 6 [2] => 9 )
    

    for your example : to get the value from inside the callback you may pass a variable to your callback by reference then edit it's value from inside the closure then use this variable outside the closure as you want as follows:

    DB::transaction(function() use (&$return) {
        $return = 'some value!';
    });
    echo $return;
    

    Conclusion :-

    this is depends on the implementation of the function/method.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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