F＃ - 警告说，我不声明类型参数明确

Question

考虑：

type Service = Object 
type Services = ConcurrentDictionary<Type, Service> 

为什么会这样：

// If we use this form, we get a compiler warning: 
type GetService<'T> = Services -> 'T 
let GetService:GetService<'T> = fun services -> 
    services.[typeof<'T>] :?> 'T 

产生警告：

“的方法或函数 '的GetService'不应该给出明确的类型参数，因为它没有声明它的类型参数明确性。“

但这并不：

let GetService<'T> (services : Services) = 
    services.[typeof<'T>] :?> 'T 

用法示例：

let someService = services |> GetService<SomeServiceType> 

如果我要纠正的第一个版本，以免得到警告，我怎么会改变的定义？

Answer 1

只要给它一个类型参数，就像错误消息所示。这应该工作：

let GetService<'T> : GetService<'T> = fun services -> 
    services.[typeof<'T>] :?> 'T