Compiling ObjC++ versus ObjC

[Michael Dickens]

On Jan 23, 2013, at 12:06 PM, Jeremy Huddleston Sequoia
<jeremyhu at macports.org> wrote:
> Yep, I think you hit the nail on the head.  In short, you pretty much want to do:
> 
> CC = clang
> CXX = clang++
> OBJCC = ${CC}
> OBJCXX = ${CXX}
> 
> ${CC} ${CPPFLAGS} ${CFLAGS} -c my.c -o my.o
> ${CXX} ${CPPFLAGS} ${CXXFLAGS} -c my.cc -o my.o
> ${CXX} ${CPPFLAGS} ${CXXFLAGS} -c my.cpp -o my.o
> ${CXX} ${CPPFLAGS} ${CXXFLAGS} -c my.cxx -o my.o
> ${OBJCC} ${CPPFLAGS} ${OBJCFLAGS} -c my.m -o my.o
> ${OBJCXX} ${CPPFLAGS} ${OBJCXXFLAGS} -c my.mm -o my.o

OK; that's what I thought too, for the best possible implementation.

Strangely enough, QMake (even in Qt5, IIRC) does not do the above; they
stop with ${OBJCC} and do not provide specific OBJCXX compiling (.m and
.mm are combined into a single OBJC set of variables).  I can easily
extend QMake to provide a separate compile chain for OBJCXX files --
I've actually already done this (in a local build, not checked in) to
get Qt4 building using -std=c++11.

My overarching goal in providing a separate compile chain is to allow
current QMake builds to work correctly without requiring OBJCXX-specific
variable setting since any other (non-MacPorts') QMake is not guaranteed
to be able to (and, generally, will not) support this feature & hence
programmers should be writing generic QMake build scripts and not
tailoring specifically to MacPorts' version of QMake.  I want to make
QMake outwardly compatible with all other QMake's, while internally
mixing things up to work better for the projects using MacPorts' QMake.

What I have done is created new OBJCXX variables that default to the CXX
versions if not explicitly set otherwise.  Since QMake's OBJC variables
default to their C counterparts, maybe I should instead set the OBJCXX
ones to the OBJC variables for defaults instead to maintain outward
compatibility?  Or, just set up a new compiler chain that uses OBJC
variables but ${CXX} for the compiler so-as to entirely do away with the
alternative OBJCXX variables?

What wisdom do y'all have here? - MLD