Define an empty Dict where the values are the subtype of an abstract type

Question

I've got an abstract type, with subtypes. I'd like to make and add to a Dict that holds the subtypes. Is this doable? What's a better way of achieving this?

Example:

abstract type Cat end

struct Lion <: Cat
   manecolour
end

struct Tiger <: Cat
   stripewidth
end

cats = Dict{Int, <:Cat}()

gives

ERROR: MethodError: no method matching Dict{Int64,var"#s3"} where var"#s3"<:Cat()

What's the more correct way of doing this?

Answer 1

Just use the abstract type as the container type: cats = Dict{Int, Cat}():

julia> cats = Dict{Int, Cat}()
Dict{Int64,Cat}()

julia> cats[1] = Lion(12)
Lion(12)

julia> cats
Dict{Int64,Cat} with 1 entry:
  1 => Lion(12)