Local functions and attributes

Daily Knowledge Drop

When using local functions, it is possible to decorate them, as well as their parameters, with attributes.

Local function

Local functions are methods of a type that are nested in another member. They can only be called from their containing member:

public class Processor
{

    // Containing method
    public void DoProcessing()
    {
        // local function/method
        void PerformInternalLogic()
        {
            Console.WriteLine("Logic being performed...");
        }

        PerformInternalLogic();
    }
}

In the above sample, the PerformInternalLogic method is a local method nested in the DoProcessing method, and can only be called from within the method.

Attributes

Method attribute

Method targeting attributes can be used on local functions:

public class Processor
{
    // Containing method
    public void DoProcessing()
    {
        // local function/method
        [Obsolete("This will be deprecated. Not useful for consumers of your method")]
        void PerformInternalLogic()
        {
            Console.WriteLine("Logic being performed...");
        }

        PerformInternalLogic();
    }
}

In the above, the Obsolete attribute was used to decorate the PerformInternalLogic method (as an indicator that the local method is obsolete and will be removed in future)

Parameter attribute

Parameter targeting attributes can also be used on local function parameters:

public class Processor
{
    // Containing method
    public void DoProcessing()
    {
        // local function/method
        [Obsolete("This will be deprecated. Not useful for consumers of your method")]
        void PerformInternalLogic()
        {
            Console.WriteLine("Logic being performed...");
        }

        // local function/method
        void PerformOtherInternalLogic([CallerMemberName] string memberName = "")
        {
            Console.WriteLine($"Logic being performed called from {memberName}");
        }

        PerformInternalLogic();

        PerformOtherInternalLogic();
    }

}

Here, the CallerMemberName attribute us applied to the parameter of the PerformOtherInternalLogic method.

Notes

A fairly niche use case, but if required, it is useful to know it is possible to add attributes to local functions.

References

8. Attributes on Local Functions

Daily Drop 204: 17-11-2022

At the start of 2022 I set myself the goal of learning one new coding related piece of knowledge a day.
It could be anything - some.NET / C# functionality I wasn't aware of, a design practice, a cool new coding technique, or just something I find interesting. It could be something I knew at one point but had forgotten, or something completely new, which I may or may never actually use.

The Daily Drop is a record of these pieces of knowledge - writing about and summarizing them helps re-enforce the information for myself, as well as potentially helps others learn something new as well.