Does C# Support Extension Properties?

Extended attributes in C#

Currently C# does not natively support extended attributes. The Roslyn compiler has not yet integrated this functionality into its standard library.

Background

In different C# versions, adding extended attributes has been discussed. However, due to concerns about its value and the need for a well-designed implementation, this feature has not yet been added.

Workarounds

Despite the lack of native support, there are some workarounds that provide limited functionality:

• TypeDescriptor: TypeDescriptor allows properties to be attached to object instances at runtime. Although it does not provide the same syntax as extended properties, it provides a way to store additional information.
• Post-processing methods: Tools such as PostSharp and Mono.Cecil can be used to dynamically add properties to classes after compilation. However, this approach may limit the compiler's optimization capabilities.

Future Outlook

Recent updates indicate that extended attributes may be supported in the future. The topic of "extending everything" has been brought up, with a focus on properties and fields. However, this feature is still in the discussion and proposal stage and is not guaranteed to be included in an upcoming C# version.

Proposed syntax

According to the proposed syntax, extension properties will use similar syntax as extension methods:

<code>public extension MyPersonExtension extends Person : IEmployee
{
    public decimal Salary { get; set; }
}</code>

This syntax allows extending a specific type with additional properties. Note that extension properties cannot add private instance members, thus ensuring the integrity of the original class structure.

The syntax and implementation of extended properties may change as the functionality is further developed and refined.

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