Trait for "can be instantiated"? (page 2)

On Tue, May 10, 2022 at 04:10:26PM +0000, Ben Jones via Digitalmars-d-learn wrote: > On Tuesday, 10 May 2022 at 16:05:15 UTC, H. S. Teoh wrote: > > Using wrapper structs, etc., for this is IMO total overkill. Just use an enum for your token types. Something like this would suffice: > > That's basically what sumtype is going to do for me, but (hopefully) more safely. Also, the token types are "user defined," my lexer just grabs everything annotated with @Token and passes those types/wrapped enums to sumtype. Ah, I see what you're trying to do. T -- Why are you blatanly misspelling "blatant"? -- Branden Robinson

May 11, 2022

Re: Trait for "can be instantiated"?

Posted by Basile B.
in reply to Ben Jones

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Basile B.

Posted in reply to Ben Jones

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On Tuesday, 10 May 2022 at 16:10:26 UTC, Ben Jones wrote:

On Tuesday, 10 May 2022 at 16:05:15 UTC, H. S. Teoh wrote:

Using wrapper structs, etc., for this is IMO total overkill. Just use an enum for your token types. Something like this would suffice:

That's basically what sumtype is going to do for me, but (hopefully) more safely. Also, the token types are "user defined," my lexer just grabs everything annotated with @Token and passes those types/wrapped enums to sumtype.

How about being more explicit in the UDA ?
The idea would be to associate the enum value to a type or not:

import std.traits;
import std.stdio;

struct Token(T);

struct Token(T...)
if (T.length == 0) { }

@Token!(string) enum str_tok;
@Token!(float)  enum float_tok;
@Token!()       enum lparen_tok;

void main()
{
    alias toks = getSymbolsByUDA!(mixin(__MODULE__), Token);

    static foreach (t; toks)
    {{
        alias U = getUDAs!(t, Token);
        alias A = TemplateArgsOf!(U);
        static if (A.length)
            pragma(msg, "add a `" ~ A[0].stringof ~ "`for `" ~ t.stringof ~ "`");
        else
            pragma(msg, "no SumType data needed for `" ~ t.stringof ~ "`");
    }}
}

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