C# method naming conventions: ToSomething vs. AsSomething

Question

As I was writing some extension methods for my business logic objects, I came to the question of renaming the conversion methods. someObject.ToAnotherObject() would go fine with the widely used object.ToString().

However LINQ, for example, mixes up both variants and I can't find a difference between them. ToDictionary(), ToList(), AsParallel(), AsQueryable(), ...

What are the differences between these two naming conventions and what should I know to decide whether to use for my own classes?

Answer 1

ToDictionary and ToList are prefixed with To because they don't necessarily preserve the structural identity of the original collection or its properties.

• Transforming a List<T> into a Dictionary<K, V> creates a collection with a whole new structure.
• Transforming a HashSet<T> into a List<T> removes the uniqueness property of sets.

Methods prefixed with As don't do any of these things - they simply provide an alternative view of the original collection. They enrich it.