• Carl Sturtivant (56/56) May 10 2017 The following compiles and runs correctly.
• Carl Sturtivant (6/6) May 10 2017 Aha, https://dlang.org/spec/struct.html#struct-destructor says

Carl Sturtivant <sturtivant gmail.com> writes:

The following compiles and runs correctly.
https://forum.dlang.org/post/tzwsohkcqrkqotbwnhjb forum.dlang.org

But if I add a destructor to the reference struct template as 
follows, it no longer compiles, and the complaints are not about 
the destructor.
```
     ~this()
     {
         ptr = null;
     }
```
refsim.d(39): Error: generated function 
refsim.reference!int.reference.opAssign (reference!int p) is not 
callable using argument types (int)
refsim.d(42): Error: generated function 
refsim.reference!int.reference.opAssign (reference!int p) is not 
callable using argument types (int)

These are complaining about lines where reference!int variables 
are assigned integers.

What's going on?

Here's the code linked to above without the destructor that works.
```
struct reference(T)
{
     T* ptr;
     this(ref T x)
     {
         ptr = &x;
     }
     import std.exception : enforce;

     ref T cnvrt()  property
     {
         enforce( ptr !is null);
         return *ptr;
     }
     ref T cnvrt(T x)  property
     {
         enforce( ptr !is null);
         return *ptr = x;
     }
     alias cnvrt this;
}

void main()
{
     int i;
     auto ri = reference!int(i);
     auto ri2 = reference!int(ri);

     assert(ri.ptr==ri2.ptr);

     i = 99;
     assert(i==ri && i==ri2 && ri==ri2);

     ri = 100;
     assert(i==ri && i==ri2 && ri==ri2);

     ri2 = 101;
     assert(i==ri && i==ri2 && ri==ri2);
}
```

Carl Sturtivant <sturtivant gmail.com> writes:

Aha, https://dlang.org/spec/struct.html#struct-destructor says 
that

An identity assignment overload is required for a struct if one 
or more of these conditions hold:

     * it has a destructor

so this is the above condition coming into play.