Re: Spec draft

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-06-17 09:20:25

[moving this to mailing list]

David Abrahams wrote
> >> (1) Dave and I talked about possible syntax for user interface. If a
> >> feature is not "free", you can just write something like this
> >>
> >> ( a.cpp <toolset>gcc:a_gcc.cpp <toolset>msvc:a_msvc.cpp ) b.cpp ...
> >>
> >> and it will get translated. (Typically conditions are made up of
> >> non-free features.)
> >
> > What's the semantic of the above?
>
> It means, take the property <source>a.cpp unless there's a
> more-specific condition in this parenthesized group, in which case,
> use the property it indicates.

This appears to be precisely the semantic of alternative, right? You have 
several items and only one of which is selected. 

> > So, property-set.create would do something smarter than just sorting all
> > properties. But it would have to sort some properties --- else much more
> > property-set instance will be created.
>
> I don't see why. It's easy to detect that two Jam lists have equal
> contents without ever sorting anything. Reasonably quickly, too.

Suppose you end up with two property sets. One contains

<define>FOO <define>BAR

and the other contains 

<define>BAR <define>FOO

Semantically, they are the same. If you've processed the first set, you can 
cache the results and do nothing about the second. If you compare them as 
strings: well, they are different.

I fact, property-set modules desperately lacks comments. The story is simple: 
I wrote it, added nice comments and accidentaly removed it. The rewritten 
version soon appeared, but I had no time for commenting for the second time 
:-(

- Volodya