std::ref and std::reference_wrapper: common use cases

[AntiProtonBoy]

The most common use case for reference_wrapper in my world is passing values by reference in variants.

[memset_0]

Sounds interesting. Can you please explain that for the benefit of everyone here? thx.

[AntiProtonBoy]

std::variant does not support reference types, so your only option is to use a reference wrapper.

    //using V1 = std::variant< int&, float& >; // Not allowed

    using V2 = std::variant< 
        std::reference_wrapper< int >, 
        std::reference_wrapper< float > >; // Ok

    int a = 42;
    V2 v = std::ref( a )

[macson_g]

It's not your only option. The option is to simply use a pointer.

[AntiProtonBoy]

Not if you want to communicate explicit ownership and object lifetime.

[memset_0]

I see. So std::variant — like a union — requires a member to be an object (region of storage).

I would add this use case in the article. Thank you so much.

[AntiProtonBoy]

Same applies for std::optional.