Examples of forward declarations (of functions) in PHP?

Question

I'm posting this because it wasn't readily apparent on Google or php.net

==> Please demonstrate several examples of the syntax for forward declaring functions, in the PHP language.

For example (in C++):

int foo(); // forward declaration

int x = foo(); // calling the function.

int foo()  // the actual implementation
{
   return 5;
}

How would this look in PHP? How about with multiple arguments? How about with default arguments? What are the best practices and why?

Answer 1

You don't need to do forward declaration in PHP, instead you need to have the function declared, in current script (even if it's after the invocation), or in any included/required script, givent that the include/require statement is executed before you call the function.

There's no forward declaration.

If on the current script, even at the end, after the invocation: it' ok

If it's on a script INCLUDEd/REQUIREd by the current script, the INCLUDE/REQUIRE statement should have been executed BEFORE invocation of the function.

If it's on a script that INCLUDE/REQUIRE the current script: it's ok (even if declared AFTER the INCLUDE/REQUIRE statement)

Answer 2

I'd say the requested example is not the best for demonstrating the need of forward declarations. Say, we need the following instead:

function foo($n) {
  echo 'Foo';
  if($n>0) bar($n-1);
}
function bar($n) {
  echo 'Bar';
  if($n>0) foo($n-1);
}
foo(200);

The code above works perfectly in PHP despite of "undefined" function bar inside foo. It appears that PHP checks function definition when it is called.

So the answer is:

1. PHP doesn't have forward declarations.
2. The function doesn't have to be defined before it appears in the text, but it must be defined before it is called.