Initialising a dictionary with duplicate keys

General Usage
3

If you, for some reason, want to have dictionary with duplicate keys you can use Base.ImmutableDict (which is however a bit tricky to use):

julia> a = Base.ImmutableDict(Base.ImmutableDict(Pair(:x, 1)), Pair(:x, 2))
Base.ImmutableDict{Symbol,Int64} with 2 entries:
  :x => 2
  :x => 1

Note that adding a new value with the same key will override the initial definition, so

julia> a[:x]
2