Multiple dispatch in Julia language

01_multiple_dispatch.jl

module MultipleDispatch

export A, A1, A2, f

# Abstract type
abstract type A end

# Concrete types
struct A1 <: A end
struct A2 <: A end

# Methods: Single dispatch
f(::Type{A1}) = "A1"
f(::Type{A2}) = "A2"

# Methods: Multiple dispatch
f(a1::Type{<:A}, a2::Type{<:A}) = f(a1) * "×" * f(a2)
f(a::Type{<:A}...) = join(f.(a), "×")

end

02.md

Single dispatch

julia> using .MultipleDispatch
julia> f(A1)
"A1"
julia> f(A2)
"A2"

Multiple dispatch

julia> f(A1, A1)
"A1×A1"
julia> f(A1, A2)
"A1×A2"
julia> f(A2, A1)
"A2×A1"
julia> f(A2, A2)
"A2×A2"

Extending

struct A3 <: A end
MultipleDispatch.f(::Type{A3}) = "A3"
f(A1, A2, A3)