= Proposal for "Do the Right Thing" Alternative Selection =

This page describes a proposal for a change to the way target alternatives are selected.

'''Note:''' the proposal is intended to be a ''pure extension''.  That is, I believe it doesn't change the semantics of any {{{bjam}}} invocation that works today -- it only changes {{{bjam}}} invocations that are currently errors into non-errors.

== Motivation ==

It seems there are a significant number of {{{bjam}}} invocations for which there is a sensible interpretation, but for which Boost.Build currently generates an error instead and refuses to build.  For example, given the following Jamfile:

{{{
lib a : a.cpp : <debug-symbols>off ;
lib a : a-dbg.cpp : <debug-symbols>on <profiling>on ;
}}}

In response to 

{{{
bjam debug-symbols=on
}}}

the result is 

{{{
error: No best alternative for ./a
    next alternative: required properties: <debug-symbols>off
        not matched
    next alternative: required properties: <debug-symbols>on <profiling>on
        not matched
}}}