Julia: Create Array from Range: Issue #4785

range_create.jl

macro NO_GC(ex)
    quote
        gc_disable()
        ret = $ex;
        gc_enable()
        gc()
    end
end

# func1: vcat(range)
function func1(a, b, inc, iter)
    tic()
    for i=1:iter
        [a:inc:b]
    end
    toc()
end
# FloatRange, no gc; Results: 1.35-1.4 seconds, 0% gc
@NO_GC func1(0,10000,0.1,1000)
# StepRange, no gc; Results: 0.2-0.25 seconds, 0% gc
@NO_GC func1(0,200000,2,1000)
# FloatRange, gc; Results: 1.8-2.0 seconds, 75% gc
func1(0,10000,0.1,1000)
# StepRange, gc; Results: 0.75-0.76 seconds, 75% gc
func1(0,200000,2,1000)

# func2: pre-allocate A, assign with A[:] = range
function func2(a, b, inc, iter)
    range = a:inc:b
    A = Array(eltype(range), length(range))
    tic()
    for i=1:iter
        A[:] = range
    end
    toc()
end
# FloatRange, no gc; Results: 0.82-0.89 seconds, 0% gc
@NO_GC func2(0,10000,0.1,1000)
# StepRange, no gc; Results: 1.94-2.00 seconds, 0% gc
@NO_GC func2(0,200000,2,1000)
# FloatRange, gc; Results: 0.76-0.78 seconds, no gc?
func2(0,10000,0.1,1000)
# StepRange, gc; Results: 1.87-1.90 seconds, no gc?
func2(0,200000,2,1000)

# func3: Pre-allocate A, devectorize assigning
function func3(a, b, inc, iter)
   temp = a:inc:b
   A = Array(eltype(temp), length(temp))
   tic()
   for i=1:iter
        ix = 1
        for j in temp
            @inbounds A[ix] = j
            ix += 1
        end
   end
   toc()
end
# FloatRange, no gc; Results: 1.19-1.22 seconds, 0% gc
@NO_GC func3(0,10000,0.1,1000)
# StepRange, no gc; Results: 0.03-0.05 seconds, 0% gc
@NO_GC func3(0,200000,2,1000)
# FloatRange, gc; Results: 1.22-1.23 seconds, no gc
@time func3(0,10000,0.1,1000)
# StepRange, gc; Results: 0.04-0.05 seconds, no gc
@time func3(0,200000,2,1000)