[英]What is the difference between = and :=
I'm sure this is straightforward but I cannot find the correct string to get a google result. 我确信这很简单,但我找不到正确的字符串来获得谷歌搜索结果。 In VB.NET what is the difference between = (equals sign) and := (colon followed by equals sign)?
在VB.NET中,=(等号)和:=(冒号后跟等号)有什么区别?
The := operator is used to pass arguments by name in VB.Net. :=运算符用于在VB.Net中按名称传递参数。 For instance take the following code
例如,请使用以下代码
Sub Foo(p1 As integer, p2 As String)
..
End Sub
Sub Test()
Foo(p2:="foo",p1:=42)
End Sub
If you look strictly at the types involved here I've passed the values out of order. 如果你仔细看看这里涉及的类型,我已经不按顺序传递了值。 But Because I bound the arguments by name using :=, the compiler will properly pass the values.
但是因为我使用:=通过名称绑定参数,编译器将正确传递值。
The = operator depends on the context in VB.Net. =运算符取决于VB.Net中的上下文。 It can be either an assignment or comparison operator.
它可以是赋值或比较运算符。 For instance
例如
Dim x = 42 ' Assignment
if x = 36 Then
'Comparison above
End if
The equal sign is used for assignment and is also a comparison operator. 等号用于赋值,也是比较运算符。 An example of assignment is
任务的一个例子是
a = 5
An example of comparison is 比较的一个例子是
if (a = 5) then
' do something here
end if
The := is used specifically for calling functions with setting particular parameters to the value by name. :=专门用于调用函数,通过名称将特定参数设置为值。 For example:
例如:
Sub studentInfo(ByVal name As String, _
Optional ByVal age As Short = 0, _
Optional ByVal birth As Date = #1/1/2000#)
Debug.WriteLine("Name = " & name & _
"; age = " & CStr(age) & _
"; birth date = " & CStr(birth))
End Sub
Normally, you would call the function like this: 通常,您可以像这样调用函数:
Call studentInfo("Mary", 19, #9/21/1981#)
But you can also call the function this way: 但你也可以这样调用函数:
Call studentInfo("Mary", birth:=#9/21/1981#)
=
is a comparison AND a set operator, but :=
is just a set operator. =
是比较AND集合运算符,但是:=
只是一个集合运算符。
Compare: If 7 = 7 Then
... 比较:
If 7 = 7 Then
...
Set: Dim myInt As Integer = 7
设置:
Dim myInt As Integer = 7
Say you have a custom object called SuperList
whose constructor takes a variable called initialCount
, then you can do things like: 假设您有一个名为
SuperList
的自定义对象,其构造函数采用名为initialCount
的变量,那么您可以执行以下操作:
Dim myList As New SuperList(initialCount:=10)
It's just sometimes easier to read a constructor when you know what values you're setting, especially if you have a constructor like SomeConstructor(12, 432, True, False, 32)
当你知道你正在设置什么值时,有时读取构造函数会更容易,特别是如果你有像
SomeConstructor(12, 432, True, False, 32)
这样的构造SomeConstructor(12, 432, True, False, 32)
It makes more sense to see SomeConstructor(monthsInYear:=12, daysInYear:=432, leapYears:True, leapDays:=False, daysInMonth:=32)
看到
SomeConstructor(monthsInYear:=12, daysInYear:=432, leapYears:True, leapDays:=False, daysInMonth:=32)
更有意义SomeConstructor(monthsInYear:=12, daysInYear:=432, leapYears:True, leapDays:=False, daysInMonth:=32)
There's probably more but this is what I got off the top of my head. 可能还有更多,但这就是我的头脑。
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