在IEnumerable上使用Seq函数 [英] Using Seq functions on an IEnumerable

问题描述

我正在尝试在IEnumerable上应用Seq函数.更具体地说，是实现ICollection和IEnumerable的System.Windows.Forms.HtmlElementCollection.

I'm trying to apply Seq functions on an IEnumerable. More specifically, it's System.Windows.Forms.HtmlElementCollection which implements ICollection and IEnumerable.

由于F#seq是IEnumerable，所以我认为我可以写

Since an F# seq is an IEnumerable, I thought I could write

let foo = myHtmlElementCollection |> Seq.find (fun i -> i.Name = "foo")

，但是编译器将一无所有，并抱怨类型'HtmlElementCollection'与类型'seq<'a>'" 不兼容.

but the compiler will have none of it, and complains that "The type 'HtmlElementCollection' is not compatible with the type 'seq<'a>'".

但是，编译器愿意在for .. in ..序列表达式中接受IEnumerable:

However, the compiler willingly accepts the IEnumerable in a for .. in .. sequence expression:

let foo = seq { for i in myHtmlElementCollection -> i } |> Seq.find (fun i -> i.Name = "foo")

我需要做些什么才能使IEnumerable像任何旧的F#seq一样被对待?

What do I need to do in order for the IEnumerable to be treated just like any old F# seq?

注意::该问题被标记为重复，但并非如此.链接的重复"是关于 untyped 序列(来自seq {for ...}表达式的seq)，而我的问题是关于 typed 序列.

NB: This question is marked as a duplicate, but it's not. The linked "duplicate" is about untyped sequences (a seq from the seq { for ... } expression), whereas my question is about typed sequences.

推荐答案

F#的类型seq<'a>等同于泛型 IEnumerable .您可以使用 Seq.cast<'a> 函数将非通用的转换为通用的:

F#'s type seq<'a> is equivalent to the generic IEnumerable<'a> in System.Collections.Generic, but not to the non-generic IEnumerable. You can use the Seq.cast<'a> function to convert from the non-generic one to the generic one:

let foo = myHtmlElementCollection
            |> Seq.cast<HtmlElement>
            |> Seq.find (fun i -> i.Name = "foo")

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