StaticArraysLite.jl

function mapreduce(f, op, a::AbstractArray; init)
    out = Ref(init)
    foreach(a) do x
        out[] = op(f(x), out[])
    end
    return out[]
end

function map(f, a::AbstractArray)
    out = similar(a, Core.Compiler.return_type(f, Tuple{eltype(a)}))
    map!(f, out, a)
    return freeze(out)
end

function map!(f, out::AbstractArray, a::AbstractArray)
    foreach(keys(out)) do i
        @inbounds out[i] = f(a[i])
    end
end

function foreach(f, a::AbstractArray)
    for i in a
        f(i)
    end
end