Fully-qualified names with nameof

[Rabadash8820]

Summary

I suggest that C# include a variant of nameof that generates an identifier's fully-qualified name. I can think of two ways the language might allow this:

1. Providing an alternate operator. I considered fullnameof or @nameof (where the @ evokes verbatim strings, which similarly modify the way strings are "expanded" in some sense).
2. Providing an additional argument to the existing operator. Something like nameof(Identifier, '.'), where the second argument instructs the compiler to expand the identifier to its fully-qualified name, with the provided character (or any const string?) separating the parts. This has the benefit of generating a fully-qualified name with any delimiter without requiring "non-const" methods like String.Split/String.Join.

Motivation

I often find myself wanting to map my namespace hierarchy to certain runtime hierarchies. For example, in the Unity game engine, I can define public methods for designers that appear nested within toolbar menus, and I typically like the nesting of the menus to match the nesting of my namespaces for easier maintenance. So if I have a method with fully qualified name MyNamespace.SubNamespace.MyType.DoStuff, I might nest it in the toolbar at "MyNamespace > SubNamespace > MyType > DoStuff". To instruct Unity to do this I declare my method as follows (Unity uses the / character to add a level of nesting:

[MenuItem($"{nameof(MyNamespace)}/{nameof(MyNamespace.SubNamespace)}/{nameof(MyType)}/{nameof(DoStuff)}")]
public static void DoStuff() => // ...

As you can see, I have to put a separate nameof operator around each part of the method's fully-qualified name. For namespaces, in particular, it would be nice if there were some way to get the fully-qualified name with one nameof call. Moreover, if I ever refactor things so that, e.g., SubNamespace becomes a top-level namespace, then all of a sudden my toolbar hierarchies will be out of sync, and there will be no compiler error/warning to tell me I'm identifying the namespace incorrectly.

Other scenarios where getting a fully-qualified type/member name might be useful include reflection, or really any scenario where someone doesn't want to "hard code" an identifier's namespaces.

[333fred]

Duplicate of #5200 and #701.

[Rabadash8820]

Damn...I promise I searched the Issues page before creating this 😅, guess I should've checked the Discussions page...

FWIW, I still think the secord-argument syntax is still worth considering. Guess I'll mention that on #701.

[jnm2]

I'm proposing making typeof(...).FullName a constant, which will help with some of these use cases: #8505

It would be great to hear in that thread about real-world use cases that support doing this, as well as real-world use cases for fullnameof that aren't addressed by that proposal and don't have a good solution today.