I refactored `MyStructure` added own implementation of malloced array based on pureRealloc/pureFree instead of dynamic array I used before and now I have error:
Error: cannot implicitly convert expression get(msg.getData()) of type const(MyStructure) to MyStructure.

What operators should I overload to let this conversion? I've tryed opCast and it fails in other call sites, also I've tried opAssign - it didn't works, what worked is wrapping in ctor - MyStruct(const_var). But using ctor is not convenient.

On Monday, 16 October 2017 at 12:00:13 UTC, drug wrote:
> I refactored `MyStructure` added own implementation of malloced array based on pureRealloc/pureFree instead of dynamic array I used before and now I have error:
> Error: cannot implicitly convert expression get(msg.getData()) of type const(MyStructure) to MyStructure.
>
> What operators should I overload to let this conversion? I've tryed opCast and it fails in other call sites, also I've tried opAssign - it didn't works, what worked is wrapping in ctor - MyStruct(const_var). But using ctor is not convenient.

The reason this doesn't work is you have some sort of non-immutable pointer, reference or array in your struct. I'm not sure why this worked before, since I have no idea what your code looks like. Hence, I can only give limited advice. Notably, the reasons this gives you a warning is because it would be unsafe to do a simple cast.

You might have turned immutable(T)[] into T[] (where T is int, byte, char, what-have-you). If this is the case, consider why this happened, and try to turn it back into immutable(T)[]. The same goes for immutable(T)*. Remember that an alias can make something immutable, so it might not be immediately obvious.

If you're fine with being unsafe, and can't find a solution like the above, consider this:

struct MyStruct {
    MyStruct getUnsafe() const {
        return cast(MyStruct)this;
    }
    alias getUnsafe this;
}

--
  Biotronic

16.10.2017 15:18, Biotronic пишет:
> On Monday, 16 October 2017 at 12:00:13 UTC, drug wrote:
>> I refactored `MyStructure` added own implementation of malloced array based on pureRealloc/pureFree instead of dynamic array I used before and now I have error:
>> Error: cannot implicitly convert expression get(msg.getData()) of type const(MyStructure) to MyStructure.
>>
>> What operators should I overload to let this conversion? I've tryed opCast and it fails in other call sites, also I've tried opAssign - it didn't works, what worked is wrapping in ctor - MyStruct(const_var). But using ctor is not convenient.
> 
> The reason this doesn't work is you have some sort of non-immutable pointer, reference or array in your struct. I'm not sure why this worked before, since I have no idea what your code looks like. Hence, I can only give limited advice. Notably, the reasons this gives you a warning is because it would be unsafe to do a simple cast.
> 
> You might have turned immutable(T)[] into T[] (where T is int, byte, char, what-have-you). If this is the case, consider why this happened, and try to turn it back into immutable(T)[]. The same goes for immutable(T)*. Remember that an alias can make something immutable, so it might not be immediately obvious.
> 
> If you're fine with being unsafe, and can't find a solution like the above, consider this:
> 
> struct MyStruct {
>      MyStruct getUnsafe() const {
>          return cast(MyStruct)this;
>      }
>      alias getUnsafe this;
> }
> 
> -- 
>    Biotronic

Hmm, I started to write reduced case and probably found the reason - I've changed slice to const data by slice to mutable data. Will investigate further. Thank you for your answer!

On 10/16/17 8:00 AM, drug wrote:
> I refactored `MyStructure` added own implementation of malloced array based on pureRealloc/pureFree instead of dynamic array I used before and now I have error:
> Error: cannot implicitly convert expression get(msg.getData()) of type const(MyStructure) to MyStructure.
> 
> What operators should I overload to let this conversion? I've tryed opCast and it fails in other call sites, also I've tried opAssign - it didn't works, what worked is wrapping in ctor - MyStruct(const_var). But using ctor is not convenient.
> 

The issue is:

int[] -> const(int)[].

This is an implicit cast from a mutable array of mutable data to a mutable array of const data. There is no way to "hook" this properly.

What you need is:

MyArray!int -> MyArray!(const(int))

But D doesn't do this implicitly. It can't, as you could implement MyArray!(const(int)) to be completely different from MyArray!int.

If you define opCast(T : MyArray!(const(T))), then it requires an explicit cast, you need an implicit one. You could use alias this, but I don't think it's as smooth.

Complicating things further, you have template functions like this:

foo(T)(const(T)[])

Where D is smart enough to pull out the T there. I don't think it works with MyArray.

-Steve