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SCons / doc / user / add-method.xml

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  <para>

  The &AddMethod; function is used to add a method
  to an environment.  It's typically used to add a "pseudo-builder,"
  a function that looks like a &Builder; but
  wraps up calls to multiple other &Builder;s
  or otherwise processes its arguments
  before calling one or more &Builder;s.
  In the following example,
  we want to install the program into the standard
  <filename>/usr/bin</filename> directory hierarchy,
  but also copy it into a local <filename>install/bin</filename>
  directory from which a package might be built:

  </para>

  <programlisting>
     def install_in_bin_dirs(env, source):
         """Install source in both bin dirs"""
         i1 = env.Install("$BIN", source)
         i2 = env.Install("$LOCALBIN", source)
         return [i1[0], i2[0]] # Return a list, like a normal builder
     env = Environment(BIN='/usr/bin', LOCALBIN='#install/bin')
     env.AddMethod(install_in_bin_dirs, "InstallInBinDirs")
     env.InstallInBinDirs(Program('hello.c')) # installs hello in both bin dirs     
  </programlisting>

  <para>
  This produces the following:
  </para>

  <screen>
    % <userinput>scons -Q /</userinput>
    cc -o hello.o -c hello.c
    cc -o hello hello.o
    Install file: "hello" as "/usr/bin/hello"
    Install file: "hello" as "install/bin/hello"
  </screen>

  <para>

  As mentioned, a pseudo-builder also provides more flexibility
  in parsing arguments than you can get with a &Builder;.
  The next example shows a pseudo-builder with a
  named argument that modifies the filename, and a separate argument
  for the resource file (rather than having the builder figure it out
  by file extension).  This example also demonstrates using the global
  &AddMethod; function to add a method to the global Environment class,
  so it will be used in all subsequently created environments.

  </para>

  <programlisting>
     def BuildTestProg(env, testfile, resourcefile, testdir="tests"):
         """Build the test program;
         prepends "test_" to src and target,
         and puts target into testdir."""
         srcfile = "test_%s.c" % testfile
         target = "%s/test_%s" % (testdir, testfile)
         if env['PLATFORM'] == 'win32':
             resfile = env.RES(resourcefile)
             p = env.Program(target, [srcfile, resfile])
         else:
             p = env.Program(target, srcfile)
         return p
     AddMethod(Environment, BuildTestProg)

     env = Environment()
     env.BuildTestProg('stuff', resourcefile='res.rc')
  </programlisting>

  <para>
  This produces the following on Linux:
  </para>

  <screen>
    % <userinput>scons -Q</userinput>
    cc -o test_stuff.o -c test_stuff.c
    cc -o tests/test_stuff test_stuff.o
  </screen>

  <para>
  And the following on Windows:
  </para>

  <screen>
    C:\><userinput>scons -Q</userinput>
    rc /fores.res res.rc
    cl /Fotest_stuff.obj /c test_stuff.c /nologo
    link /nologo /OUT:tests\test_stuff.exe test_stuff.obj res.res
    embedManifestExeCheck(target, source, env)
  </screen>

  <para>
  Using &AddMethod; is better than just adding an instance method
  to a &consenv; because it gets called as a proper method,
  and because &AddMethod; provides for copying the method
  to any clones of the &consenv; instance.
  </para>
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