Implementing global state without globals

avoidGlobals.jl

using BenchmarkTools
N=100_000

# With a let block:

let state = Ref{Bool}(false)
    global setLastShowHidden, getLastShowHidden
    function setLastShowHidden(b::Bool)
        state[] = b
    end
    function getLastShowHidden()
        state[]
    end
end
function bLet(n)
    for _ in 1:n
        if getLastShowHidden()
            setLastShowHidden(false)
        else
            setLastShowHidden(true)
        end
    end
end

# With a functor:

mutable struct ShowHidden
    last::Bool
end
function (sh::ShowHidden)(b::Bool)
    sh.last = b
end
function (sh::ShowHidden)()
    sh.last
end
const lastShowHidden = ShowHidden(false)

function bFunctor(n)
    for _ in 1:n
        if lastShowHidden()
            lastShowHidden(false)
        else
            lastShowHidden(true)
        end    
    end
end

# Benchmarks:

@btime bLet($N)
# 360.952 ns (0 allocations: 0 bytes)

@btime bFunctor($N)
# 305.837 ns (0 allocations: 0 bytes)