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<?xml version='1.0'?>
<!--
SPDX-FileCopyrightText: Copyright The SCons Foundation (https://scons.org)
SPDX-License-Identifier: MIT
-->
<!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>
<para>
The &f-link-AddMethod; function is used to add a method
to an environment. It is typically used to add a "pseudo-builder,"
a function that looks like a &Builder; but
wraps up calls to multiple other &Builders;
or otherwise processes its arguments
before calling one or more &Builders;.
</para>
<para>
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>
A pseudo-builder is useful because it gives you more flexibility
parsing arguments than you can get with a standard &Builder;.
The next example shows a pseudo-builder with a
named argument that modifies the filename, and a separate optional
argument for a 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 available 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 the target into testdir.
If the build is running on Windows, also make use of a resource file,
if supplied.
"""
srcfile = f"test_{testfile}.c"
target = f"{testdir}/test_{testfile}"
if env['PLATFORM'] == 'win32' and resourcefile:
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>
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