相当于C#typeof(IEnumerable<>)的F# [英] F# equivalent of the C# typeof(IEnumerable<>)
问题描述
我有一段代码需要确定给定类型是否实现 IEnumerable< T>
(我不在乎T)
I have a piece of code where I need to figure out if a given type implements IEnumerable<T>
(I don't care about the T)
我已经尝试过了( t:System.Type
,如果您想知道的话)
I've tried (t:System.Type
in case you wonder)
let interfaces = t.GetInterfaces()
let enumerbale =
interfaces.Any(fun t ->
t.GetGenericTypeDefinition() = typeof<IEnumerable<>>
)
但是不会编译(编译不喜欢<>)。然后我尝试了
however that won't compile (the compile doesn't like the <>). I then tried
let interfaces = t.GetInterfaces()
let enumerbale =
interfaces.Any(fun t ->
t.GetGenericTypeDefinition() = typeof<IEnumerable<'a>>
)
,但是得到警告, a是对obj的约束。我不想弄清楚是否实现了 IEnumerable< obj>
,但是 IEnumerabl<>
。
but get's a warning that 'a is constraint to obj. I Don't want to figure out if IEnumerable<obj>
is implemented but IEnumerabl<>
.
任何人都知道这是解决方案,并且btw也可以随时评论上面的代码。
Any one know's the solution and btw feel free to comment on the code above as well.
推荐答案
这应该起作用:
typedefof<System.IEnumerable<_>>
编辑
正如Tomas所指出的,这里的 _
通配符没有什么特别的; F#推断类型 obj
是此上下文中最通用的类型,因此这与使用 typedefof< System.IEnumerable< obj>相同。 >
。但是,在某些情况下,这种工作方式可能会有些障碍。例如,如果您定义接口类型I<’a,当‘a:>我<’a>> =接口端
,则您不能使用 typedefof< I< _>>
,因为 I< obj>
不满足泛型约束,F#无法推断出另一个更合适的类型。即使没有递归约束,也可能发生这种情况(例如,当时, type I 。 C#的方法,在类似的情况下效果很好。
As Tomas notes, there's nothing special about the _
wildcard here; F# infers that the type obj
is the most general applicable type in this context, so this is the same as using typedefof<System.IEnumerable<obj>>
. In some cases the way this works can be a bit of a hindrance, though. For instance, if you define an interface type I<'a when 'a :> I<'a>> = interface end
, then you can't use typedefof<I<_>>
, because I<obj>
doesn't satisfy the generic constraint and F# can't infer another more appropriate type. This can happen even without recursive constraints (e.g. type I<'a when 'a : struct and 'a :> System.ICloneable> = interface end
. This is in contrast to C#'s approach, which works perfectly fine in the analogous cases.
对于您的代码本身,我想您也想进行一些其他更改,例如在调用 GetGenericTypeDefinition
之前确保接口是通用的。这就是我编写测试函数的方式:
As to your code itself, I think you'll want to make some other changes, too, such as ensuring that the interface is generic before calling GetGenericTypeDefinition
. Here's how I'd write the test function:
(fun t -> t.IsGenericType && (t.GetGenericTypeDefinition() = typedefof<_ seq>))
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