Question

I have a dictionary data structure that must be passed around using WCF. To do that I created a member property with get and set methods. I can basicly achieve the same functionality, with this property being either a:

IDictionary<keyType, valueType>

or a

IList<KeyValuePair<keyType, valueType>>

I can see no strong reason for choosing one over the other. One mild reaons I could think of is:

IDictionary – People reading the code will think that IDictionary makes more sense, since the data structure is a dictionary, but in terms of what is passed through WCF they are all the same.

Can anyone think of a reason to choose IList? If there is none I’ll just go with IDictionary.

Answer 1

Design your interfaces based on use, not on implementation.

If the consumer of a class needs to iterate through the entire set, use IEnumerable. If they should be able to modify the result, and need index-based access, return IList. If they want specific items, and there is a single useful key value, return IDictionary.

Write your internal code this way, too 🙂