Copy a struct and its context

[Steven Schveighoffer via Digitalmars-d-learn]

On 9/12/16 4:11 PM, Ali Çehreli wrote:
> On 09/10/2016 10:44 PM, Yuxuan Shui wrote:
>> I recently noticed nested struct capture its context by reference
>> (which, BTW, is not mentioned at all here:
>> https://dlang.org/spec/struct.html#nested).

" It has access to the context of its enclosing scope (via an added 
hidden field)."

It needs to be a reference. Otherwise, you store the entire stack frame 
in the struct? That wouldn't be a "field". It also has write access to 
the context:

void foo()
{
     int i;
     struct S {
        void changeI(int newVal) { i = newVal; }
     }

     S s;
     s.changeI(10);
     assert(i == 10);
}

The documentation could be clearer.

> And bliting a struct
>> obviously doesn't do a deep copy of its context.
>>
>> So my question is, is there a way to deep copy the context of a struct?
>
> Can you show a small example? This seems to work:
>
> auto foo(int i) {
>     struct S {
>         int foo() {
>             return i;
>         }
>     }
>
>     return S();
> }
>
> void main() {
>     auto s = foo(42);
>     auto s_copy = s;
>     assert(s.foo() == 42);
>     assert(s_copy.foo() == 42);
> }

He wants to deep-copy the struct, meaning copy the context pointer data. 
Meaning if you change 'i' in s, then s_copy's foo still returns 42.

I don't think it is or should be doable.

-Steve