Am 30.01.2017 um 23:21 schrieb Brandon Williams:
On 01/30, René Scharfe wrote:
Am 30.01.2017 um 22:03 schrieb Johannes Schindelin:
It is curious, though, that an
expression like "sizeof(a++)" would not be rejected.
Clang normally warns about something like this ("warning: expression
with side effects has no effect in an unevaluated context
[-Wunevaluated-expression]"), but not if the code is part of a
macro. I don't know if that's intended, but it sure is helpful in
the case of SWAP.
Further, what would SWAP(a++, b) do? Swap a and b, and *then* increment a?
That might be a valid expectation, but GCC says "error: lvalue
required as unary '&' operand" and clang puts it "error: cannot take
the address of an rvalue of type".
René
Perhaps we could disallow a side-effect operator in the macro. By
disallow I mean place a comment at the definition to the macro and
hopefully catch something like that in code-review. We have the same
issue with the `ALLOC_GROW()` macro.
SWAP(a++, ...) is caught by the compiler, SWAP(*a++, ...) works fine.
Technically that should be enough. :) A comment wouldn't hurt, of course.
René
