• bauss (18/18) Oct 26 2017 Why is it not allowed to have empty UDAs for classes?
• Jonathan M Davis (5/23) Oct 26 2017 It worked just fine when I just tried it on my machine - both with dmd
• bauss (3/11) Oct 26 2017 Yeah I can't reproduce it right now, so I'm not even sure.
• Nicholas Wilson (3/21) Oct 26 2017 FWIW all parameterless UDA in LDC use a struct literal e.g.

bauss <jj_1337 live.dk> writes:

Why is it not allowed to have empty UDAs for classes?

Let's say we have an UDA like this:
struct Exclude { }

Then we want to put it on a class like:

 Exclude class Foo
{
     ...
}

This will fail with the following error:
Error: type Exclude has no value

But on everything else we can place an empty UDA like that ex. on 
a function:

This is okay:

 Exclude void foo()
{
     ...
}

Can someone explain to me why it's not possible with classes?

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Thursday, October 26, 2017 15:09:48 bauss via Digitalmars-d-learn wrote:
 Why is it not allowed to have empty UDAs for classes?

 Let's say we have an UDA like this:
 struct Exclude { }

 Then we want to put it on a class like:

  Exclude class Foo
 {
      ...
 }

 This will fail with the following error:
 Error: type Exclude has no value

 But on everything else we can place an empty UDA like that ex. on
 a function:

 This is okay:

  Exclude void foo()
 {
      ...
 }

 Can someone explain to me why it's not possible with classes?

It worked just fine when I just tried it on my machine - both with dmd
master and with 2.076.1. Are you using an older version of the compiler than
2.076.1? It's possible that there was a bug that was fixed.

- Jonathan M Davis

bauss <jj_1337 live.dk> writes:

On Thursday, 26 October 2017 at 21:24:43 UTC, Jonathan M Davis 
wrote:
 On Thursday, October 26, 2017 15:09:48 bauss via 
 Digitalmars-d-learn wrote:
 [...]

 It worked just fine when I just tried it on my machine - both 
 with dmd master and with 2.076.1. Are you using an older 
 version of the compiler than 2.076.1? It's possible that there 
 was a bug that was fixed.

 - Jonathan M Davis

Yeah I can't reproduce it right now, so I'm not even sure.

Nicholas Wilson <iamthewilsonator hotmail.com> writes:

On Thursday, 26 October 2017 at 15:09:48 UTC, bauss wrote:
 Why is it not allowed to have empty UDAs for classes?

 Let's say we have an UDA like this:
 struct Exclude { }

 Then we want to put it on a class like:

  Exclude class Foo
 {
     ...
 }

 This will fail with the following error:
 Error: type Exclude has no value

 But on everything else we can place an empty UDA like that ex. 
 on a function:

 This is okay:

  Exclude void foo()
 {
     ...
 }

 Can someone explain to me why it's not possible with classes?

FWIW all parameterless UDA in LDC use a struct literal e.g.
https://github.com/ldc-developers/druntime/blob/ldc/src/ldc/attributes.d#L237