Guard methods for IDictionary

[phizch]

Problem:

I tried to use Guard to ensure that a Dictionary had a minimum number of items. The expected method didn't work:

void MyMethod( Dictionary<int,string> values )
{
  // This is what I hoped to use:
  Guard.HasSizeGreaterThan( values, 1 );

  // Error   CS0121  The call is ambiguous between the following methods or properties:
  // 'Guard.HasSizeGreaterThan<T>(ICollection<T>, int, string)' 
  // and 'Guard.HasSizeGreaterThan<T>(IReadOnlyCollection<T>, int, string)'

  // This works:
  Guard.HasSizeGreaterThan( (ICollection<KeyValuePair<int, string>>)values, 1 );

  // This does not:
  Guard.HasSizeGreaterThan<ICollection<KeyValuePair<int, string>>>( values, 1 );

  // Error   CS1503  Argument 1: cannot convert from
  // 'System.Collections.Generic.Dictionary<int, string>'
  // to 'System.Span<System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<int, string>>>'
}

Typing the working one is more work than writing the if-check manually, though the exception message won't be as useful.

Suggestion:

Make an overload for the methods that take an IDictionary<TKey,TValue>

This does not work. It's ambiguous with IReadOnlyCollection<T>

Make an overload for the methods that take an ICollection

This does not work. It's ambiguous with ICollection<T>

---

I'm out of ideas except for calling the method something else. E.g. DictionaryHasCountGreaterThan. The problem is that then you must remember to use the correct method.

When C#/.NET gets support for shapes (or whatever it's getting called) something like this would be great:

shape SHasCount
{
  int Count { get; }
}
partial void HasSizeGreaterThan( SHasCount collection, int size ) 
{ /* code */ }

// or

void HasSizeGreaterThan<T>( T collection, int size ) 
        where T: class( int Count )
{ /* code */ }

Workaround:

Guard.IsGreaterThan( values.Count, 1 );