函数可以在PHP中的函数声明和函数定义之前使用吗？ [关闭]

Question

I've never seen this type of scenario in PHP. Most of the PHP examples and tutorial use the format of function calling after the declaration, but here i tried it for the first time.I think PHP use interpreter and read the code line by line. should not it generate an error in line 3 when it has not detect any function declaration before line 3?

      <?php
      $m=new m;
      echo $m->abd(17,18);
       class m
       {
           function abd($a,$b)
           {
            return($a+$b);
            }
       }
      ?>

But Output was

35

is this Possible? For reference this is the Sandbox Link you can try this code

</div>

Answer 1

From the PHP Manual

Functions need not be defined before they are referenced, except when a function is conditionally defined as shown in the two examples below.

However, it just seems like good practice to define your functions before you use them

Those two examples are

<?php

$makefoo = true;

/* We can't call foo() from here 
   since it doesn't exist yet,
   but we can call bar() */

bar();

if ($makefoo) {
  function foo()
  {
    echo "I don't exist until program execution reaches me.
";
  }
}

/* Now we can safely call foo()
   since $makefoo evaluated to true */

if ($makefoo) foo();

function bar() 
{
  echo "I exist immediately upon program start.
";
}

?>

And

<?php
function foo() 
{
  function bar() 
  {
    echo "I don't exist until foo() is called.
";
  }
}

/* We can't call bar() yet
   since it doesn't exist. */

foo();

/* Now we can call bar(),
   foo()'s processing has
   made it accessible. */

bar();

?>

For more information, this answer is sources from another SO answer