• drug (9/9) Oct 16 2017 I refactored `MyStructure` added own implementation of malloced array
• Biotronic (22/31) Oct 16 2017 The reason this doesn't work is you have some sort of
• drug (4/40) Oct 16 2017 Hmm, I started to write reduced case and probably found the reason -
• Steven Schveighoffer (17/28) Oct 16 2017 The issue is:

drug <drug2004 bk.ru> writes:

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.

Biotronic <simen.kjaras gmail.com> writes:

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

drug <drug2004 bk.ru> writes:

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!

Steven Schveighoffer <schveiguy yahoo.com> writes:

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