Of course for plain compilers var parameters can be faster, because without
smart optimizations result objects can be first allocated on the proc stack and
then copied back to the caller variable. But I had the strong feeling that this
optimization is generally done, so I never tried to avoiding result parameters.
But my current observation is that a var parameter can be indeed faster, by 10
to 20 % in my test case. (I discovered that fact by tuning my chess engine, so
it is a real life observation...)
import random, times
type
Data = tuple
a: array[16, int]
age: int
proc p1(): Data =
for i in mitems(result.a):
i = random(7)
result.age = random(7)
proc p2(res: var Data) =
for i in mitems(res.a):
i = random(7)
res.age = random(7)
proc main =
var h: Data
var sum: int
var t: float # cpuTime()
t = cpuTime()
for x in 0 .. 9999:
h = p1()
sum += h.age
echo sum
echo "p1: ", cpuTime() - t
t = cpuTime()
for x in 0 .. 9999:
p2(h)
sum += h.age
echo sum
echo "p2: ", cpuTime() - t
main()
# $ nim c -d:release ups.nim
# ~/nim-chess2 $ ./ups
# 29915
# p1: 0.000519
# 60011
# p2: 0.00042
