jkorous-apple added a comment.
Sorry, my bad, I tried just older clang version which didn't produce any error.
With reasonably up to date clang I get these:
> cat tmpl_overflow.hpp
template<int N> struct foo { short a; };
template<> struct foo<1000000000000000000 * 10240> { bool a; };
int main() {
foo<1000000000000000000 * 10240> a;
}
> ~/src/oss/llvm@master/build/bin/clang++ tmpl_overflow.hpp
tmpl_overflow.hpp:3:23: error: non-type template argument is not a constant
expression
template<> struct foo<1000000000000000000 * 10240> { bool a; };
^~~~~~~~~~~~~~~~~~~~~~~~~~~
tmpl_overflow.hpp:3:43: note: value 10240000000000000000000 is outside the
range of representable values of type 'long'
template<> struct foo<1000000000000000000 * 10240> { bool a; };
^
tmpl_overflow.hpp:6:9: error: non-type template argument is not a constant
expression
foo<1000000000000000000 * 10240> a;
^~~~~~~~~~~~~~~~~~~~~~~~~~~
tmpl_overflow.hpp:6:29: note: value 10240000000000000000000 is outside the
range of representable values of type 'long'
foo<1000000000000000000 * 10240> a;
^
2 errors generated.
I am not actually sure those error messages are correct (not constant? type
'long'?) but I am not sure it's still within the scope of your patch either.
What is interesting is that by using lower value (which is still to big for
short) I probably hit different diagnostic check and get different error:
> cat tmpl_overflow.hpp
template<int N> struct foo { short a; };
template<> struct foo<100000000000000 * 10240> { bool a; };
int main() {
foo<100000000000000 * 10240> a;
}
jankorous @ jans-imac /Users/jankorous/tmp
> ~/src/oss/llvm@master/build/bin/clang++ tmpl_overflow.hpp
tmpl_overflow.hpp:3:23: error: non-type template argument evaluates to
1024000000000000000, which cannot be narrowed to type 'int' [-Wc++11-narrowing]
template<> struct foo<100000000000000 * 10240> { bool a; };
^
tmpl_overflow.hpp:6:9: error: non-type template argument evaluates to
1024000000000000000, which cannot be narrowed to type 'int' [-Wc++11-narrowing]
foo<100000000000000 * 10240> a;
^
2 errors generated.
https://reviews.llvm.org/D42938
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