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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;
]>
<section id="sect-mergeflags"
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>Merging Options into the Environment: the &MergeFlags; Function</title>
<!--
Copyright (c) 2001 - 2017 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>
&SCons; construction environments have a &MergeFlags; method
that merges a dictionary of values into the construction environment.
&MergeFlags; treats each value in the dictionary
as a list of options such as one might pass to a command
(such as a compiler or linker).
&MergeFlags; will not duplicate an option
if it already exists in the construction environment variable.
</para>
<para>
&MergeFlags; tries to be intelligent about merging options.
When merging options to any variable
whose name ends in <varname>PATH</varname>,
&MergeFlags; keeps the leftmost occurrence of the option,
because in typical lists of directory paths,
the first occurrence "wins."
When merging options to any other variable name,
&MergeFlags; keeps the rightmost occurrence of the option,
because in a list of typical command-line options,
the last occurrence "wins."
</para>
<scons_example name="mergeflags_MergeFlags1">
<file name="SConstruct" printme="1">
env = Environment()
env.Append(CCFLAGS = '-option -O3 -O1')
flags = { 'CCFLAGS' : '-whatever -O3' }
env.MergeFlags(flags)
print env['CCFLAGS']
</file>
</scons_example>
<scons_output example="mergeflags_MergeFlags1" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
Note that the default value for &cv-link-CCFLAGS;
<!--
[TODO: for when we make CLVar public]
is a <varname>CLVar</varname>,
-->
is an internal &SCons; object
which automatically converts
the options we specified as a string into a list.
</para>
<scons_example name="mergeflags_MergeFlags2">
<file name="SConstruct" printme="1">
env = Environment()
env.Append(CPPPATH = ['/include', '/usr/local/include', '/usr/include'])
flags = { 'CPPPATH' : ['/usr/opt/include', '/usr/local/include'] }
env.MergeFlags(flags)
print env['CPPPATH']
</file>
</scons_example>
<scons_output example="mergeflags_MergeFlags2" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
Note that the default value for &cv-link-CPPPATH;
<!--
[TODO: for when we make CLVar public]
is a Python list, not a <varname>CLVar</varname>,
-->
is a normal Python list,
so we must specify its values as a list
in the dictionary we pass to the &MergeFlags; function.
</para>
<para>
If &MergeFlags; is passed anything other than a dictionary,
it calls the &ParseFlags; method to convert it into a dictionary.
</para>
<scons_example name="mergeflags_MergeFlags3">
<file name="SConstruct" printme="1">
env = Environment()
env.Append(CCFLAGS = '-option -O3 -O1')
env.Append(CPPPATH = ['/include', '/usr/local/include', '/usr/include'])
env.MergeFlags('-whatever -I/usr/opt/include -O3 -I/usr/local/include')
print env['CCFLAGS']
print env['CPPPATH']
</file>
</scons_example>
<scons_output example="mergeflags_MergeFlags3" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
In the combined example above,
&ParseFlags; has sorted the options into their corresponding variables
and returned a dictionary for &MergeFlags; to apply
to the construction variables
in the specified construction environment.
</para>
</section>
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