Re: `enum x;` - what is it?
On Wednesday, 19 August 2020 at 14:43:22 UTC, Victor Porton wrote:
On Wednesday, 19 August 2020 at 14:06:16 UTC, Victor Porton
wrote:
This declaration does compile:
enum x;
But what is it? Is it an equivalent of
enum x { }
?
What in the specification allows this looking a nonsense
enum x;
?
Oh, found: "An empty enum body (For example enum E;) signifies
an opaque enum - the enum members are unknown."
But what this "unknown" does mean? How "unknown" differs from
"none" in this context?
The specification is unclear. It does not define the meaning of
unknown. I will submit a bug report.
It means exactly what it says. The compiler doesn't know what
members are in the enum. So you can't declare a variable of it,
you can't use it directly.. you can p much only use it in
pointers.
Re: `enum x;` - what is it?
On Wednesday, 19 August 2020 at 14:06:16 UTC, Victor Porton wrote:
This declaration does compile:
enum x;
But what is it? Is it an equivalent of
enum x { }
?
What in the specification allows this looking a nonsense
enum x;
?
Oh, found: "An empty enum body (For example enum E;) signifies an
opaque enum - the enum members are unknown."
But what this "unknown" does mean? How "unknown" differs from
"none" in this context?
The specification is unclear. It does not define the meaning of
unknown. I will submit a bug report.
Re: `enum x;` - what is it?
On 8/19/20 10:06 AM, Victor Porton wrote:
This declaration does compile:
enum x;
But what is it? Is it an equivalent of
enum x { }
?
What in the specification allows this looking a nonsense
enum x;
?
I use it as a symbol for UDAs.
enum required;
struct S
{
@required int x;
}
which can then easily be found.
What is it? I have no idea. I'm just using the name.
I think it's treated as a forward declaration. Kind of like
void foo();
-Steve
Re: `enum x;` - what is it?
On Wednesday, 19 August 2020 at 14:06:16 UTC, Victor Porton wrote:
This declaration does compile:
enum x;
But what is it? Is it an equivalent of
enum x { }
?
What in the specification allows this looking a nonsense
enum x;
?
It's an enum type whose members we don't know.
So we can't declare "x var;" but we can declare "x* var;".
It's the enum version of "struct SomeExternCStruct;".
