http://blog.felixangell.com/implementing-a-programming-language-in-d-part-1/

https://www.reddit.com/r/programming/comments/3ykko7/implementing_a_programming_language_in_d_lexical/

https://news.ycombinator.com/item?id=10802610 (Go through the front page, not this link, or your votes won't count)

On 12/28/2015 04:28 PM, Walter Bright wrote:

> https://www.reddit.com/r/programming/comments/3ykko7/implementing_a_programming_language_in_d_lexical/

Although the author does not use many D idioms, I've just learned (re-learned?) anonymous enums from that code.

I've realized that with a nested anonymous enum, there is no need to (and no way of) mentioning the enum type inside a user-defined type. This can simplify the implementation:

struct S {
    enum { value }

    void foo() {
        // Look ma, no type:
        assert(value == 0);
    }
}

void main() {
    // Properly name-spaced outside of the struct:
    assert(S.value == 0);
}

As can be seen, the users of the struct still have to name-space the enum value as S.value. There is no need for an additional enum type for example like S.MyEnum.value.

Ali

On 12/28/2015 09:57 PM, Ali Çehreli wrote:

> anonymous enums

Wow! They are pretty weird:

1) The second form of the AnonymousEnumDeclaration spec is redundant, right?

  http://dlang.org/spec/enum.html#AnonymousEnumDeclaration

    enum : EnumBaseType { EnumMembers }
    enum { EnumMembers }            <-- Redundant?
    enum { AnonymousEnumMembers }

The reason is, AnonymousEnumMembers already covers EnumMembers, no?

2) Anonymous enum definitions can have types right inside the list:

AnonymousEnumMember:
    EnumMember
    Type Identifier = AssignExpression

enum {
    a,
    ulong b = 42, c,   // b and c are ulong
    s = "hello",       // an inferred string between integrals!
    x = 7, y, z
}

3) The types of x, y, and z are 'int' because 7 is an int (they don't follow the type of 'c'). However, move 's' to the end of the list or remove it altogether, then x, y, and z become ulong! Weird. Ok, I'm going to forget about this feature now. :p

Ali

On Tuesday, 29 December 2015 at 05:57:34 UTC, Ali Çehreli wrote:
> I've realized that with a nested anonymous enum, there is no need to (and no way of) mentioning the enum type inside a user-defined type. This can simplify the implementation:

Only if you intend to use enum members as manifest constants,
otherwise you're losing the type safety and explicitness
offered by named enums.
For example, I wouldn't use an anonymous enum for lexeme types.

> enum {
>     a,
>     ulong b = 42, c,   // b and c are ulong
>     s = "hello",       // an inferred string between integrals!
>     x = 7, y, z
> }

For me, it's a clear example of unnecessary over-engineering.

> However, move 's' to the end of the list or remove it altogether,
> then x, y, and z become ulong! Weird.

It's even worse than that: x, y and z will still be int (inferred from 7).
This code

> void main()
> {
>     enum {
>        a,
>        ulong b = 42, c,   // b and c are ulong
>        x = 7, y, z
>     }
>     import std.stdio, std.typecons;
>     tuple!(typeof(b), typeof(c), typeof(x)).writeln;
> }

will print

> Tuple!(ulong, ulong, int)(0, 0, 0)

which is somewhat counter-intuitive. I would suggest to remove this feature
as useless and bug-prone. The following is much clearer IMHO,
even though it's more verbose:

> enum { a }
> enum: ulong { b = 42, c }
> enum { s = "hello" }
> enum { x = 7, y, z }

Even more than that, I would also suggest to remove anonymous auto-typed enums
without an initial value from which type can be inferred, e.g.:

> enum { a } // a is an int implicitly

Again, the following is not much harder to write, but the type of 'a' is immediately clear:

> enum: int { a } // a = int.init, obviously

Although I understand that these are breaking changes,
and D is too mature to break anything (almost not being sarcastic).

On Wednesday, 30 December 2015 at 14:41:38 UTC, burjui wrote:
> On Tuesday, 29 December 2015 at 05:57:34 UTC, Ali Çehreli wrote:
>> [...]
> Even more than that, I would also suggest to remove anonymous auto-typed enums
> without an initial value from which type can be inferred, e.g.:
>
>> [...]
>
> Again, the following is not much harder to write, but the type of 'a' is immediately clear:
>
>> [...]
>
> Although I understand that these are breaking changes,
> and D is too mature to break anything (almost not being sarcastic).

anonymous enum are just not enumerations... They are more "manifest constants" available at CT. Actually their members even dont verify (is(T == enum)) ;).

They also allow not to write too much enum... and to fold in an editor.