Feature reference¶

The Waf feature system weaves additional behaviors onto existing targets (task generators) with no changes to the build scripts. The main benefits are flexibility and reduced maintenance efforts. This approach is comparable to the CSS class declarations in the web design context.

The features themselves are declared by annotating functions through a specific Python decorator function waflib.TaskGen.feature() and passing a name. Such functions then become methods bound to the Task generator class waflib.TaskGen.task_gen.

The association between feature names and methods is many-to-many; in other words a method may be used by in several features, and that a feature may reference to several methods. Here is for example how to bind the function print_hello to the feature named foo:

from waflib.TaskGen import feature
@feature('foo')
def print_hello(self):
        print("Hello, World!")

Since the function print_hello is now associated with the waflib.TaskGen.task_gen class, it becomes usable as method:

def build(bld):
        tg = bld()
        tg.print_hello()

Calling such methods directly is problematic as it interferes with partial build declarations and with target dependencies. The feature attribute enables the methods to be called exactly once before the build starts and in a purely declarative matter:

def build(bld):
        bld(features='foo')

When several methods are involved, the order of execution must be specified, else the methods are sorted by alphabetical order:

from waflib.TaskGen import feature, after_method

@feature('foo')
@after_method('print_bar')
def print_hello(self):
        print("Hello, Foo!")

@feature('bar')
def print_bar(self):
        print("Hello, Bar!")

def build(bld):
        bld(features='foo bar')

The order of method execution is unrelated to the order of the features given though. For instance, this example will print “Hello, Bar!” then “Hello, Foo!”.

The following maps represent the associations between feature methods (represented in yellow) and methods associated to other feature names. The arrows represent constraints over the order of execution.

Feature *¶

Feature asm¶

Feature c¶

Feature cprogram¶

Feature cs¶

Feature cshlib¶

Feature cxx¶

Feature cxxprogram¶

Feature cxxshlib¶

Feature d¶

Feature dshlib¶

Feature fake_lib¶

Feature fake_obj¶

Feature fc¶

Feature fcprogram¶

Feature fcprogram_test¶

Feature fcshlib¶

Feature glib2¶

Feature grep_for_endianness¶

Feature gresource¶

Feature includes¶

Feature install_task¶

Feature intltool_in¶

Feature intltool_po¶

Feature jar¶

Feature javac¶

Feature javadoc¶

Feature link_lib_test¶

Feature link_main_routines_func¶

Feature perlext¶

Feature py¶

Feature pyembed¶

Feature pyext¶

Feature qt5¶

Feature qt6¶

Feature rubyext¶

Feature seq¶

Feature skip_stlib_link_deps¶

Feature subst¶

Feature test¶

Feature test_exec¶

Feature test_scripts¶

Feature tex¶

Feature use¶

Feature uselib¶

Feature vnum¶

Feature winapp¶

Feature winphoneapp¶