Can T have a destructor when std::is_trivial_v<T> is true?

Question

#include <type_traits>

struct A
{
    ~A() {}
};

int main()
{
    static_assert(std::is_trivial_v<A>); // error   
}

It seems obvious that std::is_trivial_v<A> will be false if A has a destructor.

However, from the cppref page of std::is_trivial, there is nothing requiring A must not have a destructor.

Can T have a destructor when std::is_trivial_v<T> is true?

Answer 1

You need to go further down the rabbit hole. The cppreference page says that trivial types need to be TriviallyCopyable. If you visit that page, it has that it needs a

Trivial non-deleted destructor

and if we visit that link we have

Trivial destructor

The destructor for class T is trivial if all of the following is true:

• The destructor is not user-provided (meaning, it is either implicitly declared, or explicitly defined as defaulted on its first declaration)
• The destructor is not virtual (that is, the base class destructor is not virtual)
• All direct base classes have trivial destructors
• All non-static data members of class type (or array of class type) have trivial destructors

A trivial destructor is a destructor that performs no action. Objects with trivial destructors don't require a delete-expression and may be disposed of by simply deallocating their storage. All data types compatible with the C language (POD types) are trivially destructible.

So, yes, it needs a trivial destructor and your user provided empty one is not considered trivial.

The only way you can "write" a destructor and have it be considered trivial is to use

~ClassName() = default;