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问题描述
对于类型 类型Cow（）= class member this.Walk（） = Console.WriteLine（The cow walks。） end
我可以写一个方法强制成员约束的方法Walk像
let inline walk_the_creature creature = （^ a：（member Walk ：unit - > unit）creature） //然后做 walk_the_creature（Cow（））在这种情况下，推断类型。我无法明确地写出这样的生物参数约束。
//不编译 //查找基于这个 //程序点之前的信息的不确定类型的对象。可能需要类型注释... let inline walk_the_creature_2（生物：^ a当^ a :(成员步行：单位 - >单位））= creature.Walk（）我做错了什么？
解决方案它没有明确写出约束是问题，而是语法不够好，您可以将一个成员约束放在一个参数上，然后以通常的方式调用该成员。 walk_the_creature 和 walk_the_creature2 的主体在这里是一样的：
let inline walk_the_creature_2（生物：^ a当^ a :(成员Walk：单位 - >单位））= （^ a :(成员Walk：单位 - >单位）生物）
For a type
type Cow() = class member this.Walk () = Console.WriteLine("The cow walks.") endI can write a method which enforces a member constrain for method Walk like
let inline walk_the_creature creature = (^a : (member Walk : unit -> unit) creature) // and then do walk_the_creature (Cow())In this case the type is inferred. I am unable to explicitly write a constraint on the creature parameter like this
// Does not compile // Lookup on object of indeterminate type based on information prior to this // program point. A type annotation may be needed... let inline walk_the_creature_2 (creature:^a when ^a:(member Walk : unit -> unit)) = creature.Walk()What am I doing wrong?
解决方案It's not explicitly writing the constraints that is the issue, it's that the syntax is not so nice that you can place a member constraint on a parameter and then invoke the member in the usual way. The body of walk_the_creature and walk_the_creature2 would be the same here:
let inline walk_the_creature_2 (creature:^a when ^a:(member Walk : unit -> unit)) = (^a : (member Walk : unit -> unit) creature)
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我如何在F＃中编写此成员约束？
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