I'm trying to do some form of reflection abstraction, here's my sample code:

import std.meta;

struct Fields(T)
private static alias toField(alias e) = Field!(__traits(identifier, e));
    alias fields = staticMap!(toField, T.tupleof);

    static alias map(alias F) = staticMap!(F, fields);
    static alias filter(alias pred) = Filter!(pred, fields);

struct Field(string n)
    enum name = n;

struct Foo
    int a;

void main()
    Foo value;

    enum toName(alias e) = e.name;
    enum pred(alias e) = true;

    alias a = Fields!(Foo).filter!(pred); // works
    alias b = Fields!(Foo).map!(toName); // works

    alias c = Fields!(Foo).init.filter!(pred); // works
alias d = Fields!(Foo).init.map!(toName); // Error: alias d cannot alias an expression Fields().tuple("a")

Alias "a" and "b" compiles just fine. Alias "c" compiles as well but not alias "d", which I don't understand why. I'm fully aware that it's not possible to alias an expression, but what I want is to alias the tuple of strings that is returned.

/Jacob Carlborg

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