F＃：有括号和不带括号的类型之间的区别

Question

F＃中的type Something()和type Something有什么区别？

为什么这个片段在ASP.NET Core 1.0 F# project作品引用：

open System 
open Microsoft.AspNetCore.Hosting 
open Microsoft.AspNetCore.Builder 
open Microsoft.AspNetCore.Hosting 
open Microsoft.AspNetCore.Http 

type Startup() = 
    member this.Configure(app: IApplicationBuilder) = 
     app.Run(fun context -> context.Response.WriteAsync("Hello from ASP.NET Core!")) 

[<EntryPoint>] 
let main argv = 
    let host = WebHostBuilder().UseKestrel().UseStartup<Startup>().Build() 
    host.Run() 
    printfn "Server finished!" 
    0 

但这种失败：

open System 
open Microsoft.AspNetCore.Hosting 
open Microsoft.AspNetCore.Builder 
open Microsoft.AspNetCore.Hosting 
open Microsoft.AspNetCore.Http 

type Startup = 
    member this.Configure(app: IApplicationBuilder) = 
     app.Run(fun context -> context.Response.WriteAsync("Hello from ASP.NET Core!")) 

[<EntryPoint>] 
let main argv = 
    let host = WebHostBuilder().UseKestrel().UseStartup<Startup>().Build() 
    host.Run() 
    printfn "Server finished!" 
    0 

Answer 1

您可以通过在F＃互动键入它看到了差距：

type Parens() = 
    member this.add10 x = x + 10 

type NoParens = 
    member this.add10 x = x + 10;; 

输出：

type Parens = 
    class 
    new : unit -> Parens 
    member add10 : x:int -> int 
    end 
type NoParens = 
    class 
    member add10 : x:int -> int 
    end 

第二个类没有定义构造函数。编译器不应该允许的东西，但出于某种原因。它不会生成像C＃这样的自动构造函数。

欲了解更多信息，请查阅F＃以获取更多乐趣和获利关于classes和interfaces的网页。另外看看这个StackOverflow post

并且为了将来的参考，当有疑问的时候，打开F＃interactive，输入你想查看的两个东西之间的区别，并比较输出结果。这是一个强大的工具，你应该使用它。