F#高阶属性访问器 [英] F# Higher-order property accessors

问题描述

我刚刚将原型元组升级为记录.有一天，它可能成为真正的一堂课.同时，我要翻译这样的代码:

I just upgraded my prototyping tuple to a record. Someday it may become a real class. In the meantime, I want to translate code like this:

type Example = int * int
let examples = [(1,2); (3,4); (5,6)]
let descs = Seq.map (fst >> sprintf "%d") examples

对此:

type Example = {
  Field1 : int
  Field2 : int
  Description : string
}
let examples = [{Field1 = 1; Field2 = 2; Description = "foo"}
                {Field1 = 3; Field2 = 4; Description = "bar"}
                {Field1 = 5; Field2 = 6; Description = "baz"}]
let descs = Seq.map Description examples

问题是，当我声明Example记录时，我希望得到一个函数Description : Example -> string，但我没有.我在类上进行了一些尝试，并尝试了一些属性，但这也不起作用.我是否只是在文档中缺少某些内容，还是必须手动编写高阶访问器? (这就是我现在使用的解决方法.)

The problem is that I expected to get a function Description : Example -> string when I declared the Example record, but I don't. I've poked around a little and tried properties on classes, but that doesn't work either. Am I just missing something in the documentation or will I have to write higher-order accessors manually? (That's the workaround I'm using now.)

推荐答案

我同意最好使用某种方式将实例成员用作F#中的函数值(无需显式构造lambda函数).实际上，在F#社区中已经对此进行了几次讨论.这是一个相关的链接:

I agree it would be nice to have some way of using instance member as a function value in F# (without explicitly constructing the lambda function). This has been actually discussed a few times in the F# community. Here is one related link:

• fslang用于将属性转换为函数的UserVoice语法

该讨论中的一些建议选项是:

A few suggested options from that discussion are:

// This would turn '_' automatically into a lambda parameter
// (this looks okay in simple cases, but doesn't probably scale well)
examples |> Seq.map (_.Description)

// You would specify instance member using special '#' symbol
examples |> Seq.map (Example#Description)

因此，F#团队意识到了这一点，但是我不认为这是否真的是这个重要功能以及支持它的最佳方法是什么.

So, this is something that the F# team is aware of, but I don't think there is any conclusion whether this is actually that important feature and what would be the best way to support it.

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