c# - 比较时，没有关键字段的 VB.NET 匿名类型与 C# 匿名类型有何不同？

Question

我对此摸不着头脑，因为我不明白为什么会发生以下情况:

'//VB.NET
Dim product1 = New With {.Name = "paperclips", .Price = 1.29}
Dim product2 = New With {.Name = "paperclips", .Price = 1.29}

'compare product1 and product2 and you get false returned.

Dim product3 = New With {Key .Name = "paperclips", Key .Price = 1.29}
Dim product4 = New With {Key .Name = "paperclips", Key .Price = 1.29}

'compare product3 and product4 and you get true returned.

'//C#
var product5 = new {Name = "paperclips", Price = 1.29};
var product6 = new {Name = "paperclips", Price = 1.29};

//compare products 5 and 6 and you get true.

产品 1 和 2 发生了什么，使它们的行为不像产品 5 和 6？

Answer 1

在 C# 中，匿名类型的所有属性的行为就好像它们在 VB 中具有 Key 修饰符一样:属性是只读的，并且它们包含在相等性和哈希码计算中。

在 VB 中，没有 Key 修饰符的属性是可变的，不用于 Equals/GetHashCode 实现。

来自Anonymous Type Definition documentation :

If an anonymous type declaration contains at least one key property, the type definition overrides three members inherited from Object: Equals, GetHashCode, and ToString. If no key properties are declared, only ToString is overridden. The overrides provide the following functionality:

• Equals returns True if two anonymous type instances are the same instance, or if they meet the following conditions:

  • They have the same number of properties.
  • The properties are declared in the same order, with the same names and the same inferred types. Name comparisons are not case-sensitive.
  • At least one of the properties is a key property, and the Key keyword is applied to the same properties.
  • Comparison of each corresponding pair of key properties returns True.

• GetHashcode provides an appropriately unique GetHashCode algorithm. The algorithm uses only the key properties to compute the hash code.

• ToString returns a string of concatenated property values, as shown in the following example. Both key and non-key properties are included.