VB.NET GroupBy 元素选择器参数类型无法推断

Question

我可以在 c# 中毫无问题地做到这一点：

public class Whatever
{
    public string State { get; set; }
    public string City { get; set; }
}

var whatevers = new[] {
    new Whatever { State = "SomeState", City = "Eastville" },
    new Whatever { State = "SomeState", City = "Southville" }
};

var group = whatevers.GroupBy(
    x => x.State, x => x.City, 
    (k, v) => new { State = k, Cities = v.ToArray() }
).ToArray();

但 VB.NET 似乎存在推理问题：

Option Infer On

Public Class Whatever
    Property State As String
    Property City As String
End Class

Dim whatevers = New Whatever() {
    New Whatever With {.State = "SomeState", .City = "Eastville"},
    New Whatever With {.State = "SomeState", .City = "Southville"}
}

Dim group = whatevers.GroupBy(
    Function(x) x.State,
    Function(x) x, 'this is the problem; see below
    Function(k, v) New With {.State = k, .Cities = v.ToArray()}
).ToArray()

对于我的元素选择器，我想返回 Function(x) x.City。如果我没有指定.City，x 会正确推断为Whatever。但是，在我输入.City 的那一刻，x 无法再被推断出来。

我在这上面花了一个多小时，所以有时间来 SE。

Answer 1

一点点修复就能发挥作用。

Public Class Whatever
  Property State As String
  Property City As String
End Class

Dim whatevers = New Whatever() {
    New Whatever With {.State = "SomeState", .City = "Eastville"},
    New Whatever With {.State = "SomeState", .City = "Southville"}
}

Dim group = whatevers.GroupBy(
    Function(x As Whatever) x.State,
    Function(x As Whatever) x.City, 'this is not the problem;
    Function(k, v) New With {.State = k, .Cities = v.ToArray()}
).ToArray()