Conditional static_assert

Question

Is there an elegant way to perform a conditional static_assert in c++11

For example:

template <class T> class MyClass { COMPILE_TIME_IF( IsTypeBuiltin<T>::value) static_assert(std::is_floating_point<T>::value, "must be floating pt"); };

Have you considered using the && operator or is this not a viable alternative? — Christian Kiewiet
– Christian Kiewiet, Commented Sep 8, 2015 at 6:42
&& would work, maybe I should've rephrase the question as a 'compile time if' based on type — bendervader
– bendervader, Commented Sep 8, 2015 at 6:43
@bendervader std::is_integral<T> and std::is_floating_point<T> are exclusive. What is it that you want to achieve? — Biffen
– Biffen, Commented Sep 8, 2015 at 6:48
I want to enable the static assert if and only if the type is integral. If the user passes their own class, I do not want to assert — bendervader
– bendervader, Commented Sep 8, 2015 at 6:49
@bendervader But, if T is integral, it can't be floating point. — Biffen
– Biffen, Commented Sep 8, 2015 at 6:50

Biffen · Accepted Answer · 2015-09-08 06:55:21Z

Simple boolean logic within static_assert() should do it:

static_assert( (!std::is_fundamental<T>::value) || std::is_floating_point<T>::value, "must be floating pt" );

I.e. T is either not fundamental or it's floating point. In other words: If T is fundamental it must also be floating point.

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