like the following question, I don't want to repeat it.
https://codeshelper.com/q/10.
first of all, it is like this. Let's take a look at the following code to understand
<?php
function myfunction($v1,$v2)
{
return $v1+$v2;
}
$a=array(10,15,20);
print_r(array_reduce($a,"myfunction",5)); //50
?>
the above result is 50. So what is its process? We improve the code
function myfunction($v1, $v2)
{
var_dump($v1, $v2);
return $v1 + $v2;
}
$a = array(10, 15, 20);
print_r(array_reduce($a, "myfunction", 5)); //50
echo "\n";
then you can see the following output
int(5)
int(10)
int(15)
int(15)
int(30)
int(20)
50
the first v1 = 5recoveryv2 = 10;
the second v1 = 15 (the value returned by the previous one), v2 = 15; the value of $a [1];
the third v1 = 30 (last return value), v2 = 20; the value of $a [2];
< hr >
< hr >
now answer the subject's question:
the above example myfunction returns a numeric value, but the question of the subject run method returns a function , which is important.
now let's think of array_reduce ($class, 'App\ run', function () {}); the third function as A .
now execute
first step run (A, Session::class according to the principle of array_reduce method), return new function B (especially important, run method knowledge returns a function, the function will not execute )
second step run (B, Mysql::class), return new function C (at this time function C will be assigned to $callback )
After the
array_reduce function is executed, the final return is function C, and the last line of code $callback (); is the execution of function C.
now start to push back
// C$nextB$stepMysql::class
function($next, $step) {
call_user_func_array([new $step, 'handle'], [$next]);
};
//
call_user_func_array([new Mysql, 'handle'], [B]);
// BMysqlhandle$nextB
public function handle($next)
{
echo "<br/>Mysql Start<br/>";
$next();
echo "<br/>Mysql end<br/>";
}
// <br/>Mysql Start<br/>BB
// BA`function() {}`
call_user_func_array([new Session, 'handle'], [A]);
//
echo "<br/>Session Start<br/>";
function() {};
echo "<br/>Session End<br/>";
// BC<br/>Mysql end<br/>
//
echo "<br/>Mysql Start<br/>";
echo "<br/>Session Start<br/>";
function() {};
echo "<br/>Session End<br/>";
echo "<br/>Mysql end<br/>";
all right, the story is done.
