"Named parameter builder" pattern for template parameters

[ketmar via Digitalmars-d]

On Fri, 21 Nov 2014 13:39:42 +0000
monarch_dodra via Digitalmars-d <digitalmars-d at puremagic.com> wrote:

> D has phenomenal meta programming possibilities, and I see more
> and more templates taking more and more parameters. So I thought
> to myself, why not have a template builder pattern?
i did something similar in my iv.writer (ctfe format string parser).
once i got about ten argumnets to each template (and growing), i moved
everything to structure.

  struct WrData {
    ... fields ...

    auto set(string name, T) (in T value)
    if (__traits(hasMember, this, name))
    {
      __traits(getMember, this, name) = value;
      return this;
    }
  }

and then i can pass the struct around, changing only the fields i want,
in "pseudo-functional" style:

  template MyTpl!(WrData data) {
    ...
    MyTpl!(data.set!"field0"(value0).set!"field1"(value1));
  }

that was a real saver. but now i have to wait for GDC update, 'cause
2.065 frontend is not able to use structs as template args.
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