The definition for Dictionary
is struct Dictionary<KeyType : Hashable, ValueType> : ...
, i.e. the type of the key must conform to the protocol Hashable
. But the language guide tells us that protocols can be adopted by classes, structs and enums, i.e. not by tuples. Therefore, tuples cannot be used as Dictionary
keys.
A workaround would be defining a hashable struct type containing two Ints (or whatever you want to put in your tuple).