CODEWITHSUNDEEP
c++
Marko Sreckovic
Marko Sreckovic

Reputation: 13

No default constructor available when I put a struct in an union, but no errors if it is outside

I am trying to put RenderTargetView into an union defined below.

But when I try to do that I get the error for the no default constructor available. I am sure there should be default constructor because everything is defined.

Also if I put RenderTargetView outside of the union I am no longer getting that error. Does anyone know what is happening here ?

Eroror message:

GP::Private::ResourceView::ResourceView(void)': attempting to reference a deleted function Function was implicitly deleted because 'GP::Private::ResourceView' has a variant data member 'GP::Private::ResourceView::RTView' with a non-trivial default constructor

struct RenderTargetView
{
    static constexpr uint32_t INVALID_INDEX = static_cast<uint32_t>(-1);
    uint32_t Index = INVALID_INDEX;
};

struct FailingStruct
{
    union
    {
        RenderTargetView RTView;
    };
};

Upvotes: 1

Views: 211

Answers (1)

bolov
bolov

Reputation: 75698

A union has default non deleted constructor only if all members of the union have trivial constructors. Same for destructors. Since your struct has a member initializer this means that it doesn't have a trivial constructor this means the union constructor is deleted. You need to create special members for union where you delegate to the active member.

Or better yet use std:: variant which has all this created for you.

As for why it's simple: a union doesn't know which member is active so it cannot call the appropriate constructor/destructor.

Upvotes: 2

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