Eric Lemings wrote:
-----Original Message-----
From: Travis Vitek [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 12, 2008 4:00 PM
To: [email protected]
Subject: RE: static_assert config check
Martin Sebor wrote:
Travis Vitek wrote:
Eric Lemings wrote:
How's this for a suitable configuration check for static_assert?
// compile-only test
static_assert (sizeof (char) == 1, "impossible");
template <int I> struct S {
static_assert (I >= 0, "template parameter I must be
non-negative");
};
I've written an errily similar test already (pasted below)
I think you should probably instantiate S somewhere and it
might be a
good idea put a line break before 'struct' so that your code
conforms to our 'coding standards'.
[...]
It's probably overkill, but just as an FYI, to verify this works
both ways the test would need to be negative, i.e., named NO_XXX,
and write #define _RWSTD_NO_XXX to stdout if the negative assert
failed to fire.
So how exactly is the test supposed to write anything to stdout if it
doesn't compile? If the expression of the static_assert is false, the
program is ill-formed and the compiler is to emit a diagnostic.
I'm looking at this and if I name the test NO_STATIC_ASSERT.cpp and it
fails to compile, the macro _RWSTD_NO_STATIC_ASSERT wll be defined, so
using the NO_ prefix doesn't really buy me anything. I don't think it
would be right to make it so that if a NO_XXX test fails to
compile the
macro _RWSTD_NO_XXX will not be defined.
The only way I see to ensure that static_assert is actually
working both
ways is to write two tests, one testing for passing conditions
[STATIC_ASSERT_PASS.cpp], and the other testing for failing conditions
[STATIC_ASSERT_FAIL.cpp]. Then we would define _RWSTD_NO_STATIC_ASSERT
like so...
#if !defined (_RWSTD_NO_STATIC_ASSERT_PASS)
|| defined (_RWSTD_NO_STATIC_ASSERT_FAIL)
// STATIC_ASSERT_PASS.cpp failed to compile
// STATIC_ASSERT_FAIL.cpp compiled without error
# define _RWSTD_NO_STATIC_ASSERT
#endif
Is that overkill?
Or...you could run the negative test _first_ and if that fails (i.e.
does not fire as assertion), run the positive test which will produce
_RWSTD_NO_STATIC_ASSERT only if one or both tests failed.
Something like that. I was mainly aiming to point out that
we have both positive and negative tests. The static_assert
test clearly wasn't a good example because, as Travis noted,
it would need to be split up into two.
Martin
