CODEWITHSUNDEEP
c++templatescompiler-errorsstatic-assert
Carbon
Carbon

Reputation: 3943

How do I get type names into static_assert errors?

Assume I have this program, in which I want a bunch of specialized types and no general type. When I compile it, I'd like to get "Error: Int" instead of "Error: Z". I've tried typeof(Z) and that didn't get me anything - is there a standard trick to this?

template<class Z>
Z derp()
{
    static_assert(false, "Error: Z");
}

template <>
double derp<double>()
{
    return 5;
}


int main()
{
    double b = derp<double>();
    int r = derp<int>();
    return 0;
}

Upvotes: 3

Views: 576

Answers (1)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170203

Strictly speaking, your program is ill-formed no diagnostic required on account of that static assertion violating [temp.res]/8. But that is easily fixable. We can just define the primary template as deleted:

template<class Z>
Z derp() = delete;

template<>
double derp<double>()
{
    return 5;
}


int main()
{
    double b = derp<double>();
    int r = derp<int>();
    return 0;
}

Now the program is well formed, unless the primary specialization is actually called. Most compilers will also give the error message you want. Here's Clang 5.0:

prog.cc:14:13: error: call to deleted function 'derp'
    int r = derp<int>();
            ^~~~~~~~~
prog.cc:2:3: note: candidate function [with Z = int] has been explicitly deleted
Z derp() = delete;
  ^

Upvotes: 3

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