c# - Why doesn't/couldn't IDictionary<TKey,TValue> implement ILookup<TKey,TValue>? -

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i suppose doesn't matter, i'm curious.

if difference between dictionary , lookup 1 one-to-one , other one-to-many, wouldn't dictionary more specific/derived version of other?

a lookup collection of key/value pairs key can repeated. dictionary collection of key/value pairs key cannot repeated.

why couldn't idictionary implement ilookup?

i suspect because intention different.

ilookup<t,u> designed work collection of values. idictionary<t,u> intended work single value (that could, of course, collection).

while could, of course, have idictionary<t,u> implementations implement via returning ienumerable<u> single value, confusing, if "u" collection (ie: list<int>). in case, ilookup<t,u>.item return ienumerable<list<int>>, or should type of check ienumerable<t> value type, , "flatten" it? either way, it'd confusing, , add questionable value.


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