DU案例的名称

Question

如何填写此测试通过magic？

type DU =
  | ACaseName
  | BThereCake

let magic (q: Quotation<_>): string =
  // smallest F# code in here?

open Expecto
let subject = magic <@ ACaseName @>
Expect.equal subject "ACaseName" "Should extract the NAME of the DU case"

Answer 1

在这种情况下,以下内容将:

open Microsoft.FSharp.Quotations

let magic (q: Expr<_>): string =
  match q with 
  | Patterns.NewUnionCase(case, args) -> case.Name
  | _ -> failwith "Not a union case"

let subject = magic <@ ACaseName @>

问题是,当工会案件有一些争论时,你想做什么？例如:

type DU =
  | ACaseName
  | BThereCake of int

如果您想从中提取名称<@ BThereCake @>而不仅仅是从中提取名称<@ BThereCake(12) @>,那么您需要再添加一个案例:

let magic (q: Expr<_>): string =
  match q with 
  | DerivedPatterns.Lambdas(_, Patterns.NewUnionCase(case, args))
  | Patterns.NewUnionCase(case, args) -> case.Name
  | _ -> failwith "Not a union case"

let subject = magic <@ BThereCake @>