Function name must be a string

From Php

You can get an error like this

  Fatal error: Function name must be a string in foo.php on line 14

if you accidentally put a dollar sign at the beginning of a function name. You can also get the error if you are trying to use a non-string variable to hold the name of a function, or if you use round parens instead of square brackets when you are accessing an array.

WRONG

  $this->$foo();

WRONG

  $bar = 1234;
  $this->$bar();

WRONG

  $a = array(1, 2, 3);
  $b = $a(2);

RIGHT

  $this->foo();

ALSO RIGHT

  $bar = "foo";
  $this->$bar();

ALSO RIGHT

  $a = array(1, 2, 3);
  $b = $a[2];