Re: An Optional!T and the implementation of the underlying type's opUnary

[aliak via Digitalmars-d]

On Thursday, 26 July 2018 at 06:37:41 UTC, Simen Kjærås wrote:
On Wednesday, 25 July 2018 at 21:59:00 UTC, aliak wrote:
It needs to work with const as well and immutable too.
immutable a = 3;
auto b = -a; // is ok, should be ok with the optional as well.

Plus T can be a custom type as well with "some" definition of 
opUnary. I can't seem to find any implementation guidelines 
either so I assume opUnary or any of the ops implementation 
details is implementation defined.

Template this[0] (and CopyTypeQualifiers[1])to the rescue!


Ah! Genius!

I had no idea that using TemplateThisParameters would not 
necessitate qualifying the function in question either.


As for assigning to Optional!(immutable int), the language 
basically forbids this (cannot modify struct with immutable 
members). It would, as you say, cause problems when you can get 
a pointer to the contents.

So is this undefined behaviour?

import std.stdio;

struct S(T) {
    T value;
    void opUnary(string op)() inout {
        mixin(op ~ "cast(T)value;");
    }
}

void main() {
    immutable a = S!int(2);
    ++a;
}