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#include <type_traits>
 
template <typename> struct never_true : std::false_type { };
 
template <typename T> struct Foo
{
    static_assert(never_true<T>::value, "Can't use this.");
};
 
struct Bar;
 
int main()
{
    Foo<Bar>   x;
    Foo<int>   y;
    Foo<int[]> z;
}
 
 
 
 

prog.cpp: In instantiation of ‘struct Foo<Bar>’:
prog.cpp:15:16:   required from here
prog.cpp:8:5: error: static assertion failed: Can't use this.
prog.cpp: In instantiation of ‘struct Foo<int>’:
prog.cpp:16:16:   required from here
prog.cpp:8:5: error: static assertion failed: Can't use this.
prog.cpp: In instantiation of ‘struct Foo<int []>’:
prog.cpp:17:16:   required from here
prog.cpp:8:5: error: static assertion failed: Can't use this.
prog.cpp: In function ‘int main()’:
prog.cpp:15:16: warning: unused variable ‘x’ [-Wunused-variable]
prog.cpp:16:16: warning: unused variable ‘y’ [-Wunused-variable]
prog.cpp:17:16: warning: unused variable ‘z’ [-Wunused-variable]

Standard output is empty