“No overload takes 2 arguments” but IntelliSense shows overload with 2 arguments

问题

I'm sorry if this has been asked before, I have searched for it but can't find anything that answers my confusion.

If I write the following code, I get a compiler error saying No overload for method 'Contains' takes 2 arguments, but IntelliSense suggests that there IS an overload that takes 2 arguments (screenshot here):

string s = "Hello";
if (s.Contains('h', StringComparer.OrdinalIgnoreCase))
{
    Console.WriteLine("True!");
}

I'm passing a char as first argument and StringComparer implements IEqualityComparer so I don't get what is wrong.

Can anyone explain why I get an error?

回答1:

StringComparer implements IEqualityComparer<string> with type argument string, but the expected parameter is IEqualityComparer<char> with type argument char. The types are still incompatible.

Have a read about generic type parameters: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/generic-type-parameters

来源：https://stackoverflow.com/questions/49152427/no-overload-takes-2-arguments-but-intellisense-shows-overload-with-2-arguments