Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On 6/6/19 5:36 PM, Jonathan M Davis wrote: On Thursday, June 6, 2019 2:52:42 PM MDT Steven Schveighoffer via Digitalmars-d-learn wrote: On 6/6/19 4:49 PM, Steven Schveighoffer wrote: Oh wait! It's not empty, it has an empty string as a single member! That's definitely a bug. OK, not a bug, but not what I would have expected. From docs: "If T isn't a struct, class, or union, an expression tuple with an empty string is returned." I wonder why that behavior is there, certainly it's intentional. I guess that whoever wrote it did that rather than making it an error so that they wouldn't have to first check whether they were passing a type that even made sense. It still seems like an odd decision though. Normally, you'd just require that an appropriate type be passed. In fact, it feels like the opposite. Returning a tuple of an empty string almost guarantees you will get an error (__traits(getMember, T, "") likely is an error). I just am not sure why someone did that. A perfectly reasonable alternative would be simply to return an empty tuple. -Steve
Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On Thursday, 6 June 2019 at 20:52:42 UTC, Steven Schveighoffer wrote: On 6/6/19 4:49 PM, Steven Schveighoffer wrote: Oh wait! It's not empty, it has an empty string as a single member! That's definitely a bug. OK, not a bug, but not what I would have expected. From docs: "If T isn't a struct, class, or union, an expression tuple with an empty string is returned." I wonder why that behavior is there, certainly it's intentional. -Steve It is wrong, regardless if it is intentional. Every day people do intentional things that are wrong. The problem is that one returns a non-empty tuple and so loops will be executed on the empty string. While one can test for the empty string return there is absolutely no reason why one shouldn't just return an empty tuple as it plays correctly with the use case.
Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On Thursday, June 6, 2019 2:52:42 PM MDT Steven Schveighoffer via Digitalmars-d-learn wrote: > On 6/6/19 4:49 PM, Steven Schveighoffer wrote: > > Oh wait! It's not empty, it has an empty string as a single member! > > That's definitely a bug. > > OK, not a bug, but not what I would have expected. From docs: > > "If T isn't a struct, class, or union, an expression tuple with an empty > string is returned." > > I wonder why that behavior is there, certainly it's intentional. I guess that whoever wrote it did that rather than making it an error so that they wouldn't have to first check whether they were passing a type that even made sense. It still seems like an odd decision though. Normally, you'd just require that an appropriate type be passed. - Jonathan M Davis
Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On 6/6/19 4:49 PM, Steven Schveighoffer wrote: Oh wait! It's not empty, it has an empty string as a single member! That's definitely a bug. OK, not a bug, but not what I would have expected. From docs: "If T isn't a struct, class, or union, an expression tuple with an empty string is returned." I wonder why that behavior is there, certainly it's intentional. -Steve
Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On 6/6/19 4:43 PM, Steven Schveighoffer wrote:
On 6/6/19 4:22 PM, Amex wrote:
FieldNameTuple!T
std.traits.Fields!T
are non-empty when T is an interface!
An interface cannot contain fields and yet these return non-zero and
screws up my code. While I can filter for interfaces it makes me
wonder what else may slip through?
Is it a bug or what is going on?
Can you provide code to demonstrate? I get no fields when I do this:
interface I
{
}
import std.traits;
pragma(msg, FieldNameTuple!I);
Oh wait! It's not empty, it has an empty string as a single member!
That's definitely a bug.
-Steve
Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On 6/6/19 4:22 PM, Amex wrote:
FieldNameTuple!T
std.traits.Fields!T
are non-empty when T is an interface!
An interface cannot contain fields and yet these return non-zero and
screws up my code. While I can filter for interfaces it makes me wonder
what else may slip through?
Is it a bug or what is going on?
Can you provide code to demonstrate? I get no fields when I do this:
interface I
{
}
import std.traits;
pragma(msg, FieldNameTuple!I);
-Steve
Re: FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
On Thursday, 6 June 2019 at 20:22:26 UTC, Amex wrote: Is it a bug or what is going on? my suspicion is it is actually the pointer to the vtable getting caught up in it but idk, i didn't really look, just guessing.
FieldNameTuple!T and std.traits.Fields!T not empty for interfaces
FieldNameTuple!T std.traits.Fields!T are non-empty when T is an interface! An interface cannot contain fields and yet these return non-zero and screws up my code. While I can filter for interfaces it makes me wonder what else may slip through? Is it a bug or what is going on?
