scons_gd/scons/doc/user/add-method.xml

<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
    <!ENTITY % scons SYSTEM "../scons.mod">
    %scons;
    
    <!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
    %builders-mod;
    <!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
    %functions-mod;
    <!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
    %tools-mod;
    <!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
    %variables-mod;
    
]>

<chapter id="chap-add-method"
         xmlns="http://www.scons.org/dbxsd/v1.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">
<title>Extending &SCons;: Pseudo-Builders and the AddMethod function</title>

<!--

  MIT License

  Copyright The SCons Foundation

  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-->

  <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>

  <scons_example name="addmethod_ex1">
     <file name="SConstruct" printme="1">
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='__ROOT__/usr/bin', LOCALBIN='#install/bin')
env.AddMethod(install_in_bin_dirs, "InstallInBinDirs")
env.InstallInBinDirs(Program('hello.c')) # installs hello in both bin dirs     
     </file>
     <file name="hello.c">
int main() { printf("Hello, world!\n"); }
     </file>
  </scons_example>

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

  <scons_output example="addmethod_ex1" suffix="1">
    <scons_output_command>scons -Q /</scons_output_command>
  </scons_output>

  <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>

  <scons_example name="addmethod_ex2">
     <file name="SConstruct" printme="1">
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')
     </file>
     <file name="test_stuff.c">
int main() { printf("Hello, world!\n"); }
     </file>
     <file name="res.rc">
res.rc
     </file>
  </scons_example>

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

  <scons_output example="addmethod_ex2" suffix="1">
    <scons_output_command>scons -Q</scons_output_command>
  </scons_output>

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

  <scons_output example="addmethod_ex2" os="win32" suffix="2">
    <scons_output_command>scons -Q</scons_output_command>
  </scons_output>

  <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>

</chapter>