CODEWITHSUNDEEP
nim-lang
Alex Craft
Alex Craft

Reputation: 15366

Nim enum converter macro?

Why this string to enum converter macro fails to compile? play

import std/macros, std/strutils

macro autoconvert(TT: type[enum]) =
  let fname = "to" & $(TT)
  quote do:
    converter `fname`*(s: string): `TT` = parse_enum[`TT`](s)

type Tag* = enum movies, books
autoconvert Tag

Error

play.nim(12, 13) template/generic instantiation of `autoconvert` from here
play.nim(7, 3) Error: identifier expected, but found '"toTag"'

UPDATE:

The solution is to use ident "to" & $(TT), but why it doesn't work with just string or newLit?

Upvotes: 1

Views: 214

Answers (1)

Jason
Jason

Reputation: 495

You're using a string literal as the procedure name instead of an identifer ident("to" & $(TT)) solves the issue, but you're also using a macro instead of a template. The reason it doesnt work with a lit is that a literal is "toTag" whereas an identifer is toTag. I suggest looking at the treeRepr and repr of the result to see what is happening. The following is the afformentioned template way.

import std/strutils

template autoConvert*(TT: type[enum]) {.dirty.} =
    converter toTag*(s: string): TT = parse_enum[TT](s)

type Tag* = enum movies, books
autoconvert Tag

Upvotes: 3

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