F#模式直接针对let绑定进行匹配 [英] F# pattern match directly against let binding

问题描述

在F#中是否可以直接对let绑定进行模式匹配?

Is it possible in F# to pattern match directly against a let binding?

例如，它将在没有任何警告的情况下进行编译:

For example, this compiles without any warnings:

    let value = 
        match arg with
        | 1 -> "value1"
        | 2 -> "value2"
        | _ -> failwith "key not found"

以下内容针对匹配key2和_的行给出警告此规则将永远不会匹配" :

Whereas the following gives the warning "This rule will never be matched" against the lines matching key2 and _:

    let key1 = 1
    let key2 = 2
    let value = 
        match arg with
        | key1 -> "value1"
        | key2 -> "value2"
        | _ -> failwith "key not found"

这是因为尽管它们是不可变的，但let绑定却不同于C#const变量?

Is this because although they're immutable, the let bindings are unlike C# const variables?

推荐答案

只需使用大写字母并[<Literal>]即可，它会按预期工作.

just use capital letters and [<Literal>] them and it works as expected.

let [<Literal>] X = 0
let [<Literal>] Y = 1
let bla arg =
    match arg with
    | X -> "zero"
    | Y -> "one"
    | somethingelse -> somethingelse.ToString()

按照惯例，小写字母名称通常表示绑定到该名称的通配符.

the lower case name by convention typically means a wildcard that is bound to the name.

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