mirror of https://gitlab.com/ita1024/waf.git
55 lines
1.8 KiB
Plaintext
55 lines
1.8 KiB
Plaintext
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The Waf features are names linked to specific functions by the decorator
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:py:func:`waflib.TaskGen.feature`. The functions
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are mapped to the class :py:class:`waflib.TaskGen.task_gen` as methods.
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The association between feature names and methods is *many-to-many*, which means
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that a method may be involved in several features, and that a feature may be bound
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to several methods.
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Here is how to create and use a new feature named **foo**::
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from waflib.TaskGen import feature
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@feature('foo')
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def print_hello(self):
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print("Hello, World!")
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The function *print_hello* is now associated with the :py:class:`waflib.TaskGen.task_gen` class, which means
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that it may be used directly::
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def build(bld):
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tg = bld()
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tg.print_hello()
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The method may be called directly, and several times. If a method creates task, the same tasks will be created
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more than once, which may cause build errors. The *feature* attribute is used to have the associated
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methods called *exactly once* before the build starts::
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def build(bld):
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bld(features='foo')
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Here is a more complete example with two methods::
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from waflib.TaskGen import feature, after_method
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@feature('foo')
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@after_method('print_bar')
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def print_hello(self):
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print("Hello, Foo!")
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@feature('bar')
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def print_bar(self):
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print("Hello, Bar!")
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def build(bld):
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bld(features='foo bar')
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The order of method execution is unrelated to the order of the features given. For instance,
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this example will print "Hello, Bar!" then "Hello, Foo!". The decorators
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:py:func:`waflib.TaskGen.after` and :py:func:`waflib.TaskGen.before` are
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enforcing partial order constraints on the methods to execute.
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The following maps represent the associations betwen feature methods (represented in yellow) and
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methods associated to other feature names.
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