如何在F#的运行时创建新类型?

本文介绍了如何在F#的运行时创建新类型?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

请举例说明如何在运行时使用反射在F#中创建新类型(例如，两种笛卡尔积)?

Please give an example of how to create new type (say, two types Cartesian product) in F# at runtime with reflection?

更新

我正在寻找一种具有一流类型的语言.有人告诉我F#可以做到这一点.我没有尝试过F#，所以没有尝试.我只想看看它是怎么制成的.

I am looking for a language with first class types. I was told F# can this. I tried nothing since didn't learned F# yet. I just want to see how it's made.

推荐答案

以下F#代码采用2个值序列(在示例中为rank和suit)，并使用对数(卡)作为一系列对(卡)返回笛卡尔积.使用反射在运行时动态生成的配对类型:

The following F# code takes 2 sequences of values (rank and suit in the example) and returns the cartesian product as a sequence of pairs (cards), using a pair type dynamically generated at runtime using Reflection:

open System open System.Reflection open System.Reflection.Emit open Microsoft.FSharp.Reflection /// Creates a dynamic module via reflection let createModule () = let name = Guid.NewGuid().ToString() let d = AppDomain.CurrentDomain let a = d.DefineDynamicAssembly(AssemblyName(name), AssemblyBuilderAccess.Run) a.DefineDynamicModule(name) /// Creates a dynamic pair type using the specified x and y types let createPairType (x:Type, y:Type) = let m = createModule() let t = m.DefineType("Pair", TypeAttributes.Public ||| TypeAttributes.Class) let x = t.DefineField(x.Name, x, FieldAttributes.Public) let y = t.DefineField(y.Name, y, FieldAttributes.Public) t.CreateType() /// Creates a pair value using the specified pair type let createPairValue (pairType:Type) (x:'X, y:'Y) = let instance = Activator.CreateInstance(pairType) pairType.GetField(typeof<'X>.Name).SetValue(instance, x) pairType.GetField(typeof<'Y>.Name).SetValue(instance, y) instance /// Creates a cartesian product let createCartesianProduct (xs:'X seq, ys:'Y seq) = let pairType = createPairType (typeof<'X>,typeof<'Y>) seq { for x in xs do for y in ys -> createPairValue pairType (x, y) } /// Defines dynamic lookup operator for accessing a named field let inline (?) (x:obj) name = x.GetType().GetField(name).GetValue(x) /// Card suit discriminated union type type Suit = Club | Diamond | Heart | Spade /// Card rank discriminated union type type Rank = | One | Two | Three | Four | Five | Six | Seven | Eight | Nine | Ten | Jack | Queen | King | Ace /// Gets union case values let getUnionValues<'T>() = FSharpType.GetUnionCases(typeof<'T>) |> Seq.map (fun x -> FSharpValue.MakeUnion(x,[||]) :?> 'T) let ranks, suits = getUnionValues<Rank>(), getUnionValues<Suit>() /// Sequence of dynamically generated pairs let cards = createCartesianProduct (ranks, suits) // Paste this into F# interactive to print the generated cards for card in cards do printfn "%A %A" card?Rank card?Suit