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<?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>Pseudo-Builders: the AddMethod function</title>
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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>
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