Will this static_assert ever be triggered?

Question

template<class Int_T,class Integral,typename Best_Fit<Int_T>::type Min_Range, typename Best_Fit<Int_T>::type Max_Range> auto operator+(Integral left,const Int<Int_T,Min_Range,Max_Range>& right) ->Int<decltype(left + right.get_data())> { static_assert(std::is_integral<Integral>::value,"Non integral type is not allowed."); static_assert(std::is_integral<Int_T>::value,"Non integral type is not allowed."); auto data = left + right.get_data(); Int<decltype(left + right.get_data())> result(data); return result; }

The point is that I don't think that those two static_assert*s* will ever be triggered - even if one tries too.
So what's the answer to this Q?

I don't see why not, you could come up with a class which satisfies the constraints (Best_Fit and Int - whatever they are), but fails is_integral... — Nim
– Nim, Commented Oct 17, 2011 at 10:24
I think it is impossible to answer without definitions for Int<>, Best_Fit<> because anyone of those could trigger SFINAE — sehe
– sehe, Commented Oct 17, 2011 at 10:26
@sehe && Kerrek sorry for not providing those defs. Please find them here: stackoverflow.com/questions/7790524/… — smallB
– smallB, Commented Oct 17, 2011 at 10:30
@KerrekSB Could be promoted to a larger type, e.g. if Integral has a higher rank than Int_T. — Luc Danton
– Luc Danton, Commented Oct 17, 2011 at 10:44

Luc Danton · Accepted Answer · 2011-10-17 10:50:35Z

1

struct dummy { operator int() const { return 0; } }; // Where rhs has appropriate type dummy() + rhs;

edited Oct 17, 2011 at 10:50

answered Oct 17, 2011 at 10:45

Luc Danton

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Ayjay · Accepted Answer · 2011-10-17 10:34:18Z

0

std::string x; Int<int, 3, 5> i; auto z = x + i;

Triggered it.

answered Oct 17, 2011 at 10:34

Ayjay

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4 Comments

Luc Danton Over a year ago

That's odd. I would have expected the decltype(left + right.get_data()) to SFINAE out operator+. And in fact I can't reproduce your finding on my copy of GCC.

Ayjay Over a year ago

Well, try any type that is convertible or addable to int and even SFINAE won't help you. Eg. double.

Luc Danton Over a year ago

std::string is not such a type.

Ayjay Over a year ago

No it's not, and it looks like GCC will SFINAE std::string out while MSVC doesn't do SFINAE for this case. Even on GCC, however, a type like double will allow addition to an int while not passing is_integral.

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