return a value from closure to main method

问题

I have a closure as follows:

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

how can I return "function called" from create?

回答1:

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 . "\n";
}, 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.

回答2:

You could assign this value to a main method's variable:

public function create(){
  $var = null;
  DB::transaction(function() use (& $var){
     $var= 'function called';
     return $var;
  });
  return $var;
}

来源：https://stackoverflow.com/questions/42764839/return-a-value-from-closure-to-main-method

标签

php

closures