<?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 - 2015 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>
