Changes between Version 3 and Version 4 of AlternativeSelection

Timestamp:

Mar 26, 2007, 3:52:29 AM (19 years ago)

Author:

Dave Abrahams

Comment:

--

AlternativeSelection

@@ -3 +3 @@
 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:
+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.  
+
+=== Example 1 ===
+
+Given the following Jamfile:
 
 {{{
-lib a : a.cpp : <debug-symbols>off ;
-lib a : a-dbg.cpp : <debug-symbols>on <profiling>on ;
+lib a : a.cpp : <debug-symbols>off ;                   # alternative 1
+lib a : a-dbg.cpp : <debug-symbols>on <profiling>on ;  # alternative 2
 }}}
 
@@ -29 +31 @@
         not matched
 }}}
+ 
+My claim is that it would be more appropriate to build the 2nd alternative because it is a better match for the explicit build request.
+
+Boost.Build generates an error because the default value of the {{{<profiling>}}} feature is {{{off}}}.  It combines that default value with the explicit build request to get {{{<debug-symbols>on <profiling>off}}}, which does not match the 2nd alternative.