Linq contains confusion

Question

Hi,

I have noticed something odd with linq and the Contains method. It seems to get confused on which Contains method to call.

if (myString.Contains(strVar, StringComparison.OrdinalIgnoreCase))
{
  // Code here                  
}

The above code doesn't compile with the following error:

The type arguments for method 'System.Linq.Enumerable.Contains(System.Collections.Generic.IEnumerable, TSource, System.Collections.Generic.IEqualityComparer)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

If I remove the using linq statement it is happy with the contains (but brakes all the linq code).

What is the correct syntax to tell the compiler I want to use the String.Contains method and not Linqs?

Cheers

Answer 1

This is because there's no String.Contains(string, StringComparison) method defined in the BCL and the compiler tries to use an extension method. There's only String.Contains(string) method defined.

Answer 2

It could be because the string.Contains method takes only one parameter (a string; there is no overload of string.Contains that takes a StringComparison value), while the Enumarable.Contains extension method takes two. However, the parameters that you supply do not fit the expected input types, so the compiler gets confused.

Answer 3

What is the correct syntax to tell the compiler I want to use the String.Contains method and not Linqs?

There is no overload of String.Contains that accepts a StringComparision. You might want to use String.IndexOf(string, StringComparison):

// s is string
if(s.IndexOf(strVar, StringComparison.OrdinalIgnoreCase) >= 0) {
    // code here
}

Answer 4

As Darin Dimitrov said, String.Contains(string, StringComparison) does not exist as a method for the String type.

System.Linq.Enumerable however does contain such a signature. And a string is also an IEnumerable<char>, that's why the compiler gets confused. You would actually be able to leverage Linq and compile if you replaced the StringCompar-ison with an ICompar-er of Char:

if (myString.Contains(strVar, Comparer<Char>.Default))
{
    // Code here                  
}