nimforum mirror - Discovery rules for the 'items' iterator

Nycto (orginal) [2022-02-13T19:44:15+01:00] view original

I'm trying to figure out the compiler rules for how items are discovered. I've got some code that works when it's in a single file, but fails when spread across two files.

Here is the working code: https://play.nim-lang.org/#ix=3Pwu

But when I take that same code and spread it across two files, it fails:

# entry.nim

import groups

var builder = newGroupBuilder[string]()
echo $builder

# groups.nim

import sets

type
    GroupBuilder*[T] = object
        groups: HashSet[HashSet[T]]

proc newGroupBuilder*[T](): GroupBuilder[T] =
    result.groups = initHashSet[HashSet[T]]()

proc `$`*[T](builder: GroupBuilder[T]): string =
    result.add("{")
    for group in builder.groups:
        result.add("[")
        for item in group:
            result.add($item)
            result.add(",")
        result.add("]")
    result.add("}")

With the following error message:


/tmp/example/entry.nim(4, 6) template/generic instantiation of `$` from here
/tmp/example/groups.nim(12, 25) Error: type mismatch: got <HashSet[HashSet[system.string]]>
but expected one of:
iterator items(a: cstring): char
  first type mismatch at position: 1
  required type for a: cstring
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items(a: string): char
  first type mismatch at position: 1
  required type for a: string
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[IX, T](a: array[IX, T]): T
  first type mismatch at position: 1
  required type for a: array[IX, T]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[T: Ordinal](s: Slice[T]): T
  first type mismatch at position: 1
  required type for s: Slice[items.T]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[T: char](a: openArray[T]): T
  first type mismatch at position: 1
  required type for a: openArray[T: char]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[T: enum and Ordinal](E: typedesc[T]): T
  first type mismatch at position: 1
  required type for E: typedesc[T: enum and Ordinal]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[T: not char](a: openArray[T]): lent2 T
  first type mismatch at position: 1
  required type for a: openArray[T: not char]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[T](a: seq[T]): lent2 T
  first type mismatch at position: 1
  required type for a: seq[T]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]
iterator items[T](a: set[T]): T
  first type mismatch at position: 1
  required type for a: set[T]
  but expression 'builder.groups' is of type: HashSet[HashSet[system.string]]

expression: items(builder.groups)

I found that manually adding the items call into my loop fixes this specific example, but it's still not a workable solution because it extends to methods in the core library. For example the HashSet difference method depends on the items proc.


> nim --version
Nim Compiler Version 1.6.4 [Linux: amd64]
Compiled at 2022-02-09
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 7994556f3804c217035c44b453a3feec64405758
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8912 :: Discovery rules for the 'items' iterator