[Chapter 7] 7.2.9 Devel::SelfStubber - Generate Stubs for a SelfLoading Module
Author: Larry Wall, Tom Christiansen & Randal L. Schwartz
Date: 1999-07-02T02:01:40Z

#

| Chapter 7 The Standard Perl Library |

### 7.2.9 Devel::SelfStubber - Generate Stubs for a SelfLoading Module

    use Devel::SelfStubber;

    $modulename = "Mystuff::Grok";  # no .pm suffix or slashes
    $lib_dir = "";                  # defaults to current directory
    Devel::SelfStubber->stub($modulename, $lib_dir);   # stubs only

    # to generate the whole module with stubs inserted correctly
    use Devel::SelfStubber;
    $Devel::SelfStubber::JUST_STUBS = 0;
    Devel::SelfStubber->stub($modulename, $lib_dir);

Devel::SelfStubber supports inherited, autoloaded methods by printing the stubs you need to put in your module before the `__DATA__` token. A subroutine stub looks like this:

    sub moo;

The stub ensures that if a method is called, it will get loaded. This is best explained using the following example:

Assume four classes, A, B, C, and D. A is the root class, B is a subclass of A, C is a subclass of B, and D is another subclass of A.

>                         A
>                        / \
>                       B   D
>                      /
>                     C

If D calls an autoloaded method `moo()` which is defined in class A, then the method is loaded into class A, and executed. If C then calls method `moo()`, and that method was reimplemented in class B, but set to be autoloaded, then the lookup mechanism never gets to the `AUTOLOAD` mechanism in B because it first finds the `moo()` method already loaded in A, and so erroneously uses that. If the method `moo()` had been stubbed in B, then the lookup mechanism would have found the stub, and correctly loaded and used the subroutine from B.

So, to get autoloading to work right with classes and subclasses, you need to make sure the stubs are loaded.

The SelfLoader can load stubs automatically at module initialization with:

    SelfLoader->load_stubs();

But you may wish to avoid having the stub-loading overhead associated with your initialization.[8] In this case, you can put the subroutine stubs before the `__DATA__` token. This can be done manually, by inserting the output of the first call to the `stub()` method above. But the module also allows automatic insertion of the stubs. By default the `stub()` method just prints the stubs, but you can set the global `$Devel::SelfStubber::JUST_STUBS` to `0` and it will print out the entire module with the stubs positioned correctly, as in the second call to `stub()`.

> [8] Although note that the `load_stubs()` method will be called sooner or later, at latest when the first subroutine is being autoloaded - which may be too late, if you're trying to `moo()`.

At the very least, this module is useful for seeing what the SelfLoader thinks are stubs; in order to ensure that future versions of the SelfStubber remain in step with the SelfLoader, the SelfStubber actually uses the SelfLoader to determine which stubs are needed.

7.2.8 DB_File - Access to Berkeley DB |  | 7.2.10 diagnostics - Force Verbose Warning Diagnostics