通用参数的空列表

发布于 2024-12-06 23:50:43 字数 349 浏览 0 评论 0原文

规范第 15.3 节提到序列 < > 中间有空格是允许的形式。它表示通用参数的空列表，这允许出现以下奇怪的情况。

type A() = class end
let a = new A< >()

为什么这是允许的？由于泛型类型可以在省略类型参数的情况下实例化，这是否是一种类型检查优化？

原文

Section 15.3 of the spec mentions the sequence < > with intervening whitespace is an allowed form. It indicates an empty list of generic arguments, which allows for the following oddity.

type A() = class end
let a = new A< >()

Why is this allowed? Since generic types can be instantiated with type args omitted, is this a type checking optimization of sorts?

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星軌x 2024-12-13 23:50:43

我同意 Ramon 的观点，它使事情更加一致，因为您可以将非泛型类型视为泛型 arity 0 类型的退化情况。对于泛型 arity“重载”的类型，这允许您更明确地说明您所指的类型：

type T(o:obj) = class end
type T<'t>(t:'t) = class end

let t = T("test")
let t' = T< >("test")
let t'' = T<_>("test")

在不仔细考虑重载解析的情况下，t 的类型不一定很明显，但完全清楚 t' 和t'' 有。

I agree with Ramon that it makes things more consistent, in that you can treat non-generic types as a degenerate case of types of generic arity 0. In the case of types which are "overloaded" by generic arity, this allows you to be more explicit about which type you're referring to:

type T(o:obj) = class end
type T<'t>(t:'t) = class end

let t = T("test")
let t' = T< >("test")
let t'' = T<_>("test")

Without thinking carefully about overload resolution, it's not necessarily obvious what type t has, but it's completely clear what types t' and t'' have.

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