On Tuesday, 30 March 2021 at 13:28:55 UTC, novice3 wrote:
Hello.
When i adapt C code, i see new type creation:
typedef void* Xobj;
Or code like this:
struct _Xobj;
typedef struct _Xobj *Xobj;
I want create derived type in D, found std.typecons.Typedef
template, and write:
alias Xobj = Typedef!(void*, (void*).init);
But compiler use long type name in error messages, like this:
Error: function test6.foo(Typedef!(void*, null, null) obj) is
not callable using argument types (void*)
cannot pass argument bad of type void* to parameter
Typedef!(void*, null, null) obj
This messages dont help me understand, which type should i use.
What i should change?
Or Typedef template should be changes?
Any Typedef alternatives?
The typedef in C in D is just an alias:
```
alias Xobj = void*;
```
Xobj can then be used interchangeably with void*, so all void*
arguments accept Xobj and all Xobj arguments accept void*.
If you want a type-safe alias that makes all void* arguments
accept Xobj but not Xobj arguments to accept void* you can use
`Typedef` like you linked. However using this language built-in
feature is much simpler and cheaper in terms of resource usage
and compile time + always results in the fastest code: (there is
no conversions at all)
```
enum Xobj : void*;
```
This allows explicit conversion in both ways using cast, but only
allows implicit conversion from Xobj to void*, not from void* to
Xobj:
```
void* x = someValue;
Xobj y = cast(Xobj)x; // ok
x = y; // ok
y = x; // error (need explicit cast)
```
