Re: [Boost-build] [PATCH] -ftemplate-depth

From: Jurko Gospodnetić (jurko.gospodnetic_at_[hidden])
Date: 2008-07-30 07:44:29

   Hi Markus,

>> actions compile.c++
>> {
>>     $(CONFIG_COMMAND) -x cxx -c -std strict_ansi -nopure_cname 
>> -noimplicit_include -timplicit_local -ptr "$(<[1]:D)/cxx_repository" 
>> $(OPTIONS) "-pending_instantiations "$(TEMPLATE_DEPTH) -D$(DEFINES) 
>> -I"$(INCLUDES)" -o "$(<)" "$(>)"
>> }
> 
> Won't that expand to '-pending_instantiations' (instead of nothing) when 
> TEMPLATE_DEPTH is empty?

   Nope, that is what the quotes are for - to make the 
"-pending_instantiations " text be joined to the TEMPLATE_DEPTH variable 
expansion.

   In Boost Jam (as well as the original Jam) when you do xxx$(var) you 
get all the values of 'var', with each one of them prefixed by 'xxx'.

   Had we written:

   -pending_instantiations $(TEMPLATE_DEPTH)

   (note the missing quotes) Boost Jam would have interpreted this as 
"string literal '-pending_instantiations' and then all the values of 
TEMPLATE_DEPTH".

   With the quotes:

   "-pending_instantiations "$(TEMPLATE_DEPTH)

   (note the added quotes) Boost Jam interprets this as "all the values 
of TEMPLATE_DEPTH, each one prefixed with '-pending_instantiations'" 
which comes out as nothing in case TEMPLATE_DEPTH is an empty list.

   You can see the same technique applied for expanding DEFINES & 
INCLUDES variables in the original action code.

   Hope this helps.

   Best regards,
     Jurko Gospodnetić