Toolset inheritance

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-01-20 09:36:00

I was thinking about reuse of toolset definitions when declaring other
toolsets. The conclusion is that it's probably quite simple. Basically,
toolset can:

- change some variables (for example Kylix can redefine
COMPILER_NAME and LINKER_NAME, provided base borland toolset uses those),
- add some flags
- rewrite some rules

I think that V2 heavily uses generators, this is the right unit of 
inheritance. We have provide some means to inherit generator. For example,
borland toolset contains:

generators.register-compiler borland.compile : CPP : OBJ : <toolset>borland ;

Toolset for kylix can contain:

toolset.inherit-generator borland.compile ;

This would create new generator "kylix.compile" which will be equal to
"borland.compile" except that required properties will contain <toolset>kylix
instead of <toolset>borland.

All flags relevant to this generator will be inherited too. Lastly, all rules
will be imported. E.g if borland.jam had:

actions compile
{
$(COMPILER_NAME) ....
}

then the kylix module will get its own copy of this rule, which will use the 
COMPILER_NAME variable defined in the kylix module.

I guess there should also be a convenience rule, which will inherit all
generators from other module.

Does it sound reasonable?

- Volodya