使用内部自动类型定义 Nim 概念时遇到问题

问题描述

我无法定义包含 auto 类型的概念。 Nim 似乎在抱怨 type T = auto 变成了 untyped。

这是一个基本取自 run it online here) 的最小示例 (from the docs)：

import sugar,typetraits

type
  Functor[A] {.explain.} = concept f
    type MatchedGenericType = genericHead(typeof(f))
      # `f` will be a value of a type such as `Option[T]`
      # `MatchedGenericType` will become the `Option` type
    
    # f.val is A
      # The Functor should provide a way to obtain
      # a value stored inside it
    
    type T = auto
    map(f,A -> T) is MatchedGenericType[T]
      # And it should provide a way to map one instance of
      # the Functor to an instance of a different type,given
      # a suitable `map` operation for the enclosed values

import options
echo Option[int] is Functor # should print true but doesn't!

# The above came straight from
# <https://nim-lang.org/docs/manual_experimental.html#concepts-generic-concepts-and-type-binding-rules>
  

proc f(x: Functor) = echo "yes!"
f(some(1))

这是错误的相关部分（除了文档说 Option[int] is Functor 应该是 true 但不是）：

proc map[T,R](self: Option[T]; callback: proc (input: T): R): Option[R]
  first type mismatch at position: 2
  required type for callback: proc (input: T): R{.closure.}
  but expression 'proc (i0: A): T' is of type: type proc (i0: int): untyped{.closure.}

我基本上是从文档中复制粘贴。我做错了什么？

解决方法

我不知道如何回答您关于在概念体中使用 auto 的问题，我的直觉是这不太可能奏效。

我可以通过删除自动内容以及使用 typedef 参数调用 map 来使您的示例工作吗？我也不明白。

import sugar,typetraits

type
  Functor[A] {.explain.} = concept f,type t
    type MatchedGenericType = genericHead(typeof(f))
      # `f` will be a value of a type such as `Option[T]`
      # `MatchedGenericType` will become the `Option` type
    
    # f.val is A
      # The Functor should provide a way to obtain
      # a value stored inside it
    
    #type T = auto
    proc mapto[T](x:t):MatchedGenericType[T] = map(f,default(A->T))
    #map(f,A->T) is MatchedGenericType[T]
      # And it should provide a way to map one instance of
      # the Functor to a instance of a different type,given
      # a suitable `map` operation for the enclosed values

import options
echo Option[int] is Functor # prints true

# The above came straight from <https://nim-lang.org/docs/manual_experimental.html#concepts-generic-concepts-and-type-binding-rules>.
  
proc f(x: Functor) = echo "yes!"
f(some(1))