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Diffstat (limited to 'bitbake/doc')
| -rw-r--r-- | bitbake/doc/user-manual/user-manual-metadata.xml | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/bitbake/doc/user-manual/user-manual-metadata.xml b/bitbake/doc/user-manual/user-manual-metadata.xml index 3864c00..a57fe0c 100644 --- a/bitbake/doc/user-manual/user-manual-metadata.xml +++ b/bitbake/doc/user-manual/user-manual-metadata.xml @@ -792,6 +792,82 @@ </itemizedlist> </para> </section> + + <section id='automatically-mapping-functions-within-the-context-of-a-class'> + <title>Automatically Mapping Functions Within the Context of a Class</title> + + <para> + Through coding techniques and the use of + <filename>EXPORT_FUNCTIONS</filename>, BitBake supports + automatic mapping for functions within the context of + a class. + </para> + + <para> + To understand the benefits of this feature, consider the basic scenario + where a class defines a function and your recipe inherits the class. + In this basic scenario, your recipe has access to the function in the + class by way of inheritance and can freely call and use the function + as defined in the class. + However, if you need to have a modified version of that function + in your recipe you are limited to using either your modified version + of the function or using "prepend_" or "_append" operators to add + code to be executed before or after the original function in the + class. + Your recipe cannot use both versions of the fucntion. + </para> + + <para> + Function mapping allows you to access both your custom function + function that is defined in the recipe and the original function that + is defined in the class. + You have this access all from within your recipe. + To accomplish this, you need some things in place: + <itemizedlist> + <listitem><para> + The class needs to define the function as follows: + <literallayout class='monospaced'> + <classname>_<functionname> + </literallayout> + For example, if you have a class file + <filename>bar.bbclass</filename> and a function named + <filename>do_foo</filename>, the class must define the function + as follows: + <literallayout class='monospaced'> + bar_do_foo + </literallayout> + </para></listitem> + <listitem><para> + The class needs to contain the <filename>EXPORT_FUNCTIONS</filename> + statement as follows: + <literallayout class='monospaced'> + EXPORT_FUNCTIONS <functionname> + </literallayout> + For example, continuing with the same example, the + statement in the <filename>bar.bbclass</filename> would be + as follows: + <literallayout class='monospaced'> + EXPORT_FUNCTIONS do_foo + </literallayout> + </para></listitem> + <listitem><para> + You need to call the function appropriately from within your + recipe. + Continuing with the same example, + your recipe would call the <filename>do_foo</filename> function + from the recipe by referring to it as + <filename>bar_do_foo</filename>. + To call your modified version of the function as defined in your + recipe, call it as <filename>do_foo</filename>. + </para></listitem> + </itemizedlist> + With these conditions met, your single recipe + can freely choose between the original function + as defined in the class file and the modified function in your recipe. + If you do not set up these conditions, you are limited to using one function + or the other. + </para> + </section> </section> <section id='tasks'> |
