Is this really intended??

[Paul Backus]

On Sunday, 11 October 2020 at 00:16:53 UTC, claptrap wrote:
> Arn't structs supposed to be default initialised?
>
> But in a constructor a struct member is not? If you write to a 
> field in a struct member suddenly it is considered initialised?
>
> And yet it's OK to call a method on the struct that is not 
> initialised, but if you do it's still uninitialised?
>
> Why should
>
> foo.i = 0;
> foo.reset();
>
> Result in the compiler changing whether it's OK to call 
> opAssign?

The first assignment to a member inside a constructor is 
considered initialization so that you can use constructors to 
initialize immutable members:

struct Example
{
     immutable int i;
     this(int i)
     {
         this.i = i; // ok, initialization
         this.i = 42; // error, assignment to immutable variable
     }
}

One consequence of this is that the first assignment does not 
call opAssign, since opAssign isn't used for initialization.

I agree that this is kind of a hack. A more principled way to 
handle this would be to introduce a separate syntax for 
initialization, like `let this.i = i` or `this.i := i`.