DU案例名稱

Question

如何通過填寫magic來完成此測試？

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

在這種情況下，下面會做什麼：

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 @> 

的問題是，你要當工會的情況下有一定的論據做什麼。例如：

type DU = 
    | ACaseName 
    | BThereCake of int 

如果你想從<@ BThereCake @>提取名稱，而不是僅僅從<@ BThereCake(12) @>，那麼你需要添加更多的情況：

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 @>