具有通用参数类型的函数 [英] Functions with generic parameter types

问题描述

我想弄清楚如何定义一个可以处理多种类型参数的函数（例如int和int64）。据我了解，函数重载在F＃中是不可能的（当然编译器会抱怨）。例如下面的函数。

  let sqrt_int = function 
 | n：int  - > int（sqrt（float n））
 | n：int64  - > int64（sqrt（float n））
  

编译器当然会抱怨语法无效（类型约束在模式匹配中似乎不被支持），但我认为这说明了我想实现的功能：一个函数，它对多个参数类型进行操作并返回相应类型的值。我有一种感觉，这是可能的F＃使用泛型/类型推理/模式匹配的一些组合，但语法已经躲过了我。我也尝试使用：？运算符（动态类型测试）和当在模式匹配块中使用子句时，但是这样仍会产生各种错误。

在语言方面，我可能很想在这里做一些不可能的事情，所以请让我知道是否有其他解决方案。 解决方案

p>重载通常是类型推导语言的bug（至少在类似F＃的情况下，类型系统的功能不足以包含类型类）。在F＃中有许多选择：

• 在方法（类型的成员）上使用重载，在这种情况下，重载很有效就像在其他.Net语言中一样（您可以临时使用超载成员，提供的调用可以通过参数的数量/类型加以区分）
  
• 使用inline，^和静态成员约束，用于在函数上进行特别重载（这是大多数需要处理int / float /等等的各种数学运算符;这里的语法很奇怪，除了F＃库以外，这种语法很少使用）


• 通过传递额外的操作字典参数来模拟类型类（这是INumeric在其中一个F＃PowerPack库中对一般用于任意用户定义类型的各种数学算法进行的操作） li>
  
• 返回到动态类型（传入'obj'参数，执行动态类型测试，为错误类型抛出运行时异常）
  

对于您的特定示例，我可能会说t使用方法重载：

  type MathOps = 
 static member sqrt_int（x：int）= x |> float |> sqrt |> int 
 static member sqrt_int（x：int64）= x |> float |> sqrt |> int64 
 
 let x = MathOps.sqrt_int 9 
 let y = MathOps.sqrt_int 100L 
  

I am trying to figure out how to define a function that works on multiple types of parameters (e.g. int and int64). As I understand it, function overloading is not possible in F# (certainly the compiler complains). Take for example the following function.

let sqrt_int = function
    | n:int   -> int (sqrt (float n))
    | n:int64 -> int64 (sqrt (float n))

The compiler of course complains that the syntax is invalid (type constraints in pattern matching are not supported it seems), though I think this illustrates what I would like to achieve: a function that operates on several parameter types and returns a value of the according type. I have a feeling that this is possible in F# using some combination of generic types/type inference/pattern matching, but the syntax has eluded me. I've also tried using the :? operator (dynamic type tests) and when clauses in the pattern matching block, but this still produces all sorts errors.

As I am rather new to the language, I may very well be trying to do something impossible here, so please let me know if there is alternative solution.

解决方案

Overloading is typically the bugaboo of type-inferenced languages (at least when, like F#, the type system isn't powerful enough to contain type-classes). There are a number of choices you have in F#:

• Use overloading on methods (members of a type), in which case overloading works much like as in other .Net languages (you can ad-hoc overload members, provided calls can be distinguished by the number/type of parameters)
• Use "inline", "^", and static member constraints for ad-hoc overloading on functions (this is what most of the various math operators that need to work on int/float/etc.; the syntax here is weird, this is little-used apart from the F# library)
• Simulate type classes by passing an extra dictionary-of-operations parameter (this is what INumeric does in one of the F# PowerPack libraries to generalize various Math algorithms for arbitrary user-defined types)
• Fall back to dynamic typing (pass in an 'obj' parameter, do a dynamic type test, throw a runtime exception for bad type)

For your particular example, I would probably just use method overloading:

type MathOps =
    static member sqrt_int(x:int) = x |> float |> sqrt |> int
    static member sqrt_int(x:int64) = x |> float |> sqrt |> int64

let x = MathOps.sqrt_int 9
let y = MathOps.sqrt_int 100L

这篇关于具有通用参数类型的函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！