Understanding the usage of php variable functions

Recently I saw a variable assigned a value from the name of a function as a string in a project. I thought the program was wrong, and I found out after asking my colleagues.

This is variable function, I'm sweating instantly. By the way, record it:

function func() {
  return 'hello,world!';
 }
$myFunction = 'func';

When we create a custom function and understand the usage of variable functions, in order to ensure that the function called by the program exists, we often first Use function_exists to determine whether the function exists.

The same method_exists can be used to detect whether a class method exists.

if (function_exists($myFunction )){
    echo 'exists';
}

Whether the class is defined, class_exists can be used.

class MyClass{
}
// 使用前检查类是否存在
if (class_exists('MyClass')) {
    $myclass = new MyClass();
}

There are many such checking methods in PHP, such as whether the file existsfile_existsetc.

$filename = 'test.txt';
if (!file_exists($filename)) {
    echo $filename . ' not exists.';
}

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