使用F#Reflection将两个对象与默认的IComparable实现进行比较

问题描述

给定F#中的两个对象，有一种方法可以使用它们的IComparable方法进行比较，假设它们都是相同的子类型，并且IComparable是针对其公共子类型实现的.

Given two objects in F#, is there a way to use their IComparable method to compare them, assuming they are both of the same sub-type and that IComparable is implemented for their common sub-type.

我想用伪代码实现的目标:

What I am trying to achieve in pseudo-code :

    let tycompare (o1 : obj) (o2 : obj) : int option =
        let (ty1, ty2) = (o1.GetType(), o2.GetType())
        if ty1 <> ty2 then
            None
        else
            if IComparable is implemented on ty1 then
                o1.CompareTo(o2) |> Some
            else
                None

我知道此帖子，但我认为这无助于回答我的问题直接提问.

I am aware of this post but I do not think it helps answering my question directly.

推荐答案

您还可以使用Option.bind简洁地编写此代码，但这非常适合模式匹配.

You could also write this more tersely with Option.bind, but this is a good fit for pattern matching.

我们可以定义活动模式用于匹配IComparable.

We can define an active pattern for matching IComparable.

let (|IsComparable|) (obj : obj) = 
    match obj with
    | :? IComparable as comparable -> Some(comparable)
    | _ ->  None

F#使您可以在let绑定中使用活动模式，以便更清楚地传达功能的意图.

F# lets you use active patterns in let bindings, so that the intent of function is more clearly conveyed.

let compare (IsComparable o1) (IsComparable o2) =        
    match (o1, o2) with
    | (Some o1, Some o2) when 
        o1.GetType() = o2.GetType() -> Some(o1.CompareTo(o2))
    | _ -> None

这也可以压缩(不使用活动模式-@kaefer):

This can also be compacted (without the active-pattern - @kaefer) :

let compare (o1 : obj) (o2: obj) = 
    match (o1, o2 ) with
    | (:? System.IComparable as o1), (:? System.IComparable as o2) when 
        o1.GetType() = o2.GetType() -> Some(o1.CompareTo(o2))
    | _ -> None

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