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Thread-Topic: High performance function autoloading
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Date: Mon, 20 May 2019 17:17:49 +0000
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Subject: High performance function autoloading
From: theodorejb@outlook.com (Theodore Brown)

Every time function autoloading been brought up in the past, there=0A=
have been concerns about performance issues when calling a global=0A=
function from inside a namespace. E.g. calling `strlen` in a loop=0A=
would become far slower if every call has to trigger the autoloader.=0A=
=0A=
But isn't it extremely rare to override global functions in a=0A=
namespace? And even if they are overridden, how common is it to call=0A=
an overridden function in the same namespace that exists in a=0A=
different file?=0A=
=0A=
Would it be possible to handle this rare case with a per-file option=0A=
like `declare(root_fallback=3D0);`?=0A=
=0A=
Consider the following code examples:=0A=
=0A=
# example_1.php=0A=
```php=0A=
namespace Foo;=0A=
=0A=
echo strlen('test');=0A=
// PHP would first check if Foo\strlen exists. If not, it would check=0A=
// whether \strlen exists. Since it does, it would call the built-in=0A=
// function as expected without triggering the autoloader.=0A=
```=0A=
=0A=
# example_2.php=0A=
```php=0A=
namespace Foo;=0A=
=0A=
function strlen(string $str) {...}=0A=
=0A=
echo strlen('test');=0A=
// PHP would first check if Foo\strlen exists. Since it is defined in=0A=
// the same file, it would be called without falling back to the=0A=
// global function or triggering the autoloader.=0A=
```=0A=
=0A=
# example_3.php=0A=
```php=0A=
namespace Foo;=0A=
=0A=
use function Bar\strlen;=0A=
=0A=
echo strlen('test');=0A=
// PHP would first check if Bar\strlen exists. If not, it would=0A=
// trigger the autoloader rather than falling back to the global=0A=
// function. The same thing would occur for any qualified function=0A=
// call. E.g. without "use function" the following could be written:=0A=
echo \Bar\strlen('test');=0A=
```=0A=
=0A=
# example_4.php=0A=
```php=0A=
namespace Foo;=0A=
=0A=
echo my_function('test');=0A=
// PHP would first check if Foo\my_function exists. If not, it would=0A=
// check whether \my_function exists. If not, the autoloader would be=0A=
// triggered.=0A=
```=0A=
=0A=
# example_5.php=0A=
```php=0A=
declare(root_fallback=3D0);=0A=
=0A=
namespace Foo;=0A=
=0A=
echo strlen('test');=0A=
// PHP would first check if Foo\strlen exists. If not, it would=0A=
// trigger the autoloader rather than falling back to the global=0A=
// function, since root fallback is disabled in the file.=0A=
```=0A=
=0A=
What are your thoughts about this approach?=0A=
=0A=
Personally I would rarely have to disable root fallback, since I like=0A=
to group functions in a single file per namespace. But it seems like=0A=
this would be a good way to enable function autoloading that works=0A=
with namespaces spread across multiple files and doesn't slow down=0A=
performance.=