On Tuesday, 23 de August de 2011 13:00:51 Konstantin Tokarev wrote: > 23.08.2011, 12:58, "Thiago Macieira" <thi...@kde.org>: > > And the other requirement is that QT_STL be binary compatible with > > QT_NO_STL. > Could you explain why this requirement is needed?
I think I could ask back: why not require it?
It's not difficult to have Qt be binary compatible in those two versions. All
it
requires is that the Qt non-inline API never have anything that is disabled by
QT_NO_STL. That means all functions must be present if that is defined, which
in turn means no function can carry a non-inline STL type in their signature.
Tag types might be permitted, but in most cases tags exist for template and
inline code, so I don't think it's a problem.
The reason I personally want this is that I'd like to compile Qt without
#include'ing the STL headers everywhere. Nothing wrong with them -- they're
just non-trivial in size, meaning the compilation time is bigger. For someone
who needs to compile Qt several times a day and no longer has access to a nice
compile farm, this could come in very handy.
Moreover, imagine an embedded device that wants to save space in the minimal
base system: they could choose to compile Qt and all of their applications
without STL, thus saving a few hundred kilobytes of libstdc++. But user
applications could still use STL if they wanted and interoperate with Qt, only
triggering the install of that lib.
Finally, I've been reading the C++ ABI mailing list and there are several
teams there, from different compilers. They are cooperating to make the same
ABI between their compilers. That doesn't mean, however, that one compiler's
STL implementation works on another.
So a hypothetical scenario is that a device maker chooses to use a different
compiler for the base system, like RVCT for ARM devices, than the free
compiler that is offered to third-party users in the SDKs (normally GCC). The
STL implementations are incompatible, so they build the base system without
STL support, but GCC-built 3rd-party applications can use STL and interoperate
with Qt.
--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
Software Architect - Intel Open Source Technology Center
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