Using namespace in if / else statements

Question

I am manipulating the same file to manage two external api classes.

One api class is based on namespaces, the other one is not.

What I would like to do is something like this:

if($api == 'foo'){
   require_once('foo.php');
}
if($api == 'bar'){
   require_once('bar.php');
   use xxxx\TheClass;
}

The problem is that when I do so, the following error message is returned:

Parse error: syntax error, unexpected T_USE in etc...

Question 1: Do I have to use two different files to manage the two classes or is it possible to manage both while using namespaces in the document? From what I see, it does not seem to be.

Question 2: Why namespaces could not be used inside if() statements?

Thank you for your help

Answer 1

Please see Scoping rules for importing

The use keyword must be declared in the outermost scope of a file (the global scope) or inside namespace declarations. This is because the importing is done at compile time and not runtime, so it cannot be block scoped.

All use does is import a symbol name into the current namespace. I would just omit the import and use the fully qualified class name, eg

switch ($api) {
    case 'foo' :
        require_once('foo.php');
        $someVar = new SomeClass();
        break;
    case 'bar' :
       require_once('bar.php');
       $someVar = new \xxxx\TheClass();
       break;
   default :
       throw new UnexpectedValueException($api);
}

You can also simply add the use statement to the top of your script. Adding it does not commit you to including any files and it does not require the symbol to be known, eg

use xxxx\TheClass;

switch ($api) {
    case 'foo' :
        require_once('foo.php');
        $someVar = new SomeClass();
        break;
    case 'bar' :
       require_once('bar.php');
       $someVar = new TheClass(); // imported above
       break;
   default :
       throw new UnexpectedValueException($api);
}

Answer 2

Use statements should be placed before any executable code (you can have namespaces, classes, functions and constants definitions). Actually it can, just have to be placed unconditionally in some namespace, so no ifs or inside functions. Also don't be afraid of putting use at the top, it does not load any class or instantiate object. it acts only as alias that is used when encountered later during execution.

As for having them in one file, it is possible to have many namespaces and even global namespace in one file:

<?php   
namespace
{
    class myclass{}
}
namespace mynamespace 
{
    class myclass{}
}

But I strongly discourage such "management" of code. Each class should have it's own file.