“属性”在此属性上是什么意思？

Question

[property: Obsolete]
static int X
{
    get { return 42; }
}

In the code above, what purpose does the word "property" serve? The code seems to work the same way if I replace [property: Obsolete] with [Obsolete]. And although "property" is coloured blue in Visual Studio, it does not appear in the list of C# keywords: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/

Answer 1

The Attribute specification defines this as an attribute target .

Certain contexts permit the specification of an attribute on more than one target. A program can explicitly specify the target by including an attribute_target_specifier. When an attribute is placed at the global level, a global_attribute_target_specifier is required. In all other locations, a reasonable default is applied, but an attribute_target_specifier can be used to affirm or override the default in certain ambiguous cases (or to just affirm the default in non-ambiguous cases).

It also states that in many cases, like the one you mention, it is permitted but not necessary.

In other contexts, inclusion of an attribute_target_specifier is permitted but unnecessary. For instance, a class declaration may either include or omit the specifier type.

Answer 2

This is an attribute target specification .

In your code the use of it is not really necessary, since there is just one allowed target for that attribute at that place. The Obsolete attribute can be placed on a type, method or a property, but if placed on a property, only the property target specifier is allowed (and used implicitly).

The most practical use for this is the assembly target specifier, where you can set assembly configuration through attributes:

[assembly: AssemblyProduct("Foo bar")]

You can set the allowed targets on your custom attributes using AttributeUsage .