Why GCC 5.3.0 gives warning when binding reference to “this” pointer

Question

Here is the minimal example:

class A
{
    A* const& this_ref;
public:
    A() : this_ref(this) {}
};

GCC 5.3.0 gives warning:

Answer 1

Is this a temporary then?

To be precise, this is not temporary, but a temporary is created here.

Firstly, this is prvalue,

The following expressions are prvalue expressions:

• the this pointer;

Secondly, temporary object will be created when binding reference to a prvalue,

Temporary objects are created when a prvalue is materialized so that it can be used as a glvalue, which occurs (since C++17) in the following situations:

• binding a reference to a prvalue

That's why GCC gives warning, because this_ref is bound to a temporary created. (And then become dangled later, which leads to UB.)