Julia types

julia_types.jl

# Define holder for Int, parametrized with number.
type I{N}
  x::Int
end

# We have access to type parameter in runtime.
show{N}(x::I{N}) = "N(x=$(x.x) N=$N)"

# We can specialize implementation by type parameter.
show(x::I{1}) = "1(x=$(x.x))"

println(show(I{3}(1)))
#> N(x=1 N=3)

println(show(I{1}(1)))
#> 1(x=1)

# Define type parametrized by type
type H{T}
  v::T
end

show{T}(x::H{T}) = "generic($x)"

# We can have function specialized for concrete type
show(x::H{Int}) = "Int($x)"

# We can have function specialized for all subtypes of String
show{T<:String}(x::H{T}) = "String($x)"

# And even specialization for the specific subtype
# (note that ASCIIString <: String)
show(x::H{ASCIIString}) = "ASCIIScting($x)"

println(show(H(1)))
#> Int(H{Int64}(1))

println(show(H("a")))
#> ASCIIScting(H{ASCIIString}("a"))

println(show(H{String}("a")))
#> String(H{String}("a"))

type D{K,V}
  k::K
  v::V
end

show{K,V}(kv::D{K,V}) = "{K=$K V=$V}($kv)"

println(show(D(1, "a")))