Question

I am writing an extension method where I happen to need the field name that the extension method is needed within the extension method. I can not figure out how to do this.

My code:

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Extension method:

public static Validate Demand<T>(this T parameter) {     string name = ...     var field = GetField(parameter);     return Validation.CreateValidation(parameter, field, name); } 

Use case:

void SomeMethod(T someParameter) {    someParameter.Demand(); } 

I want name to hold someParameter.

Answer 1

You can’t. It would be nice in a few cases, particularly for argument checking, but it’s just not possible. As an example of where it would be handy, I have this method:

internal static void ThrowIfNull<T>(this T argument, string name)     where T : class {     if (argument == null)     {         throw new ArgumentNullException(name);     } } 

which I have to call with:

foo.ThrowIfNull('foo'); 

It’s better than nothing, but it would be nice not to have to supply the ‘foo’ bit. Unfortunately, there’s just no way of doing it. You could probably write a post-build IL rewriter which determined how the method was called and rebuilt it from that, but that’s rather more work than the benefit, I suspect 🙂