nameof should support keyword type aliases

[colejohnson66]

nameof is a contextual keyword. As such, it is prone to sharp edges such as cryptic error messages when used incorrectly.

For example, nameof(int) gives CS1525: "[i]nvalid expression term 'int'". This is confusing as I didn't write an expression, but a type keyword. It gets worse as nameof(int.TryParse) works just fine (gives "TryParse"). If I want nameof(int) to give "Int32", I must write nameof(Int32).

This also clashes with the existing lookup rules for typeof; typeof(int) returns the same as typeof(System.Int32).

An open question would be: should nameof(int) give "int" or "Int32". I'd argue the latter, as "name of" returns "the name of a program entity as a constant string", and "int" does not exist at runtime. So it's not an "entity", but a keyword.

[CyrusNajmabadi]

Note: this is intentional. The purpose of nameof is to give the actual name of something. Note that int is more an alias, and in that regard, i'd expect it to work as nameof does on aliases here.

Also, nameof exists entirely to link a symbol and a reference to its name so that when one changes, the other can be updated. That concern doesn't exist with Int32 as it's not going to be renamed. If you're using nameof purely to reference the thing, then it's also sensible to just reference the thing in a way that clearly indicates waht it will be replaced with.

For example, nameof(int) gives CS1525: "[i]nvalid expression term 'int'". This is confusing as I didn't write an expression, but a type keyword.

All types are expressions in the language. That's what enables writing a type on the left hand side of a dot for example :)

This also clashes with the existing lookup rules for typeof; typeof(int) returns the same as typeof(System.Int32).

Sure, but typeof isn't nameof. It's specifically intended to be about getting the end runtime type. nameof is not that. It's about allowing you to specify the name in way that isn't a string. so you can type nameof(Int32) and get compile time checking, vs "Int32". In particular, we've had people ask for the exact opposite. That nameof(int) return "int" since it's what is in the nameof.

Having the rules be simple/clear/consistent is def valuable here. When you see nameof you just need to look at the last actual name in the arguments, and that's what you'll get as the string value. No question on how things will be interpreted.

As mentioned above, this is also very relevant for aliases. if you have using X = System.Int32; then nameof(X) gives you "X" not "Int32". This is a very lexical/syntactic construct. Not a semantic one. Intentionally so.