c# Dictionary: making the Key case-insensitive through declarations

When you add an element to the outer dictionary, you’ll likely create a new instance of the nested dictionary, add it at this point, making use of the overloaded constructor that takes an IEqualityComparer<TKey>.

_customRecordSet.Add(0, new Dictionary<string, CustomClass>(StringComparer.InvariantCultureIgnoreCase));

Update 08/03/2017: Anecdotally, I read somewhere (I think in “Writing High-Performance .NET Code”) that StringComparer.OrdinalIgnoreCase is more efficient when simply wanting to disregard the case of characters. This, however, is entirely unfounded by myself so YMMV.