VB中特性构造函数是否支持命名参数？语法疑问求助

Great question—you’re right that VB does support named parameters for attribute constructors, but there’s a tiny syntax gotcha specific to attributes that’s tripping you up here. Let’s break this down:

1. Constructor Named Parameters vs. Attribute Property Initialization #

First, let’s clarify two separate things in your attribute declaration:

• Constructor parameters: Your FullName attribute’s constructor takes FirstName and LastName. Using := for these (like LastName:="moreno") is totally valid—this is how you specify named parameters for the constructor, just like you do when instantiating a regular object.
• Attribute properties: The Hey property is a separate member of your attribute class. For setting properties in attribute declarations, VB uses = instead of :=. The := syntax is only for constructor arguments; property initialization in attributes uses the standard assignment operator.

2. Fixed Version of Your Code #

The mistake is in how you’re setting the Hey property. Here’s the corrected attribute line:

<FullName(LastName:="moreno", FirstName:="John", Hey = "joe")>
Public Class Example
    Public Sub Test()
        ' This part is already correct!
        Dim x = New FullName(LastName:="moreno", FirstName:="john")
    End Sub
End Class

Your direct object instantiation (New FullName(...)) works because that’s standard VB syntax where := works for constructor named parameters. Attributes have their own rules for property initialization, which is why you need to switch to = there.

3. Quick Recap #

• Use ParameterName:=Value for constructor arguments in attribute declarations.
• Use PropertyName=Value for setting attribute properties in the same declaration.

内容的提问来源于stack exchange，提问作者jmoreno