Understanding the Cost of Virtualization

fast.jl

type ChildA
end

type ChildB
end

increment(c::ChildA, x) = x + 1
increment(c::ChildB, x) = x + 2

type Container
    i::Int
    ca::ChildA
    cb::ChildB
end

function increment(c::Container, x)
    if c.i == 1
        return increment(c.ca, x)
    elseif c.i == 2
        return increment(c.cb, x)
    else
        error("bad model selector")
    end
end

function run(n)
    sum = 0
    container = Container(1, ChildA(), ChildB())
    for i in 1:n
        sum = increment(container, sum)
    end
    container.i = 2
    for i in 1:n
        sum = increment(container, sum)
    end
    @show sum
end

run(10)

@time run(10000000)

other.jl

abstract Parent

type ChildA <: Parent
end

type ChildB <: Parent
end

incrementA(x) = x + 1
incrementB(x) = x + 2

type Container
    p::Parent
end

function increment(c::Container, x)
    if isa(c.p, ChildA)
        return incrementA(x)
    elseif isa(c.p, ChildB)
        return incrementB(x)
    end
end

function run(n)
    sum = 0
    container = Container(ChildA())
    for i in 1:n
        sum = increment(container, sum)
    end
    container.p = ChildB()
    for i in 1:n
        sum = increment(container, sum)
    end
    @show sum
end

run(10)

@time run(10000000)

slow.jl

abstract Parent

type ChildA <: Parent
end

type ChildB <: Parent
end

increment(c::ChildA, x) = x + 1
increment(c::ChildB, x) = x + 2

type Container
    p::Parent
end

increment(c::Container, x) = increment(c.p, x)

function run(n)
    sum = 0
    container = Container(ChildA())
    for i in 1:n
        sum = increment(container, sum)
    end
    container.p = ChildB()
    for i in 1:n
        sum = increment(container, sum)
    end
    @show sum
end

run(10)

@time run(10000000)