📂Julia

Julia's Short Circuit

Overview

In Julia, && and || not only perform logical AND and OR operations but also execute short-circuit evaluation¹. For instance, A && B returns true only if both A and B are true, but in reality, if A is false, there is no need to check whether B is true or false; A && B is false. Short-circuit evaluation essentially skips checking B. Skipping the calculation for B can lead to performance improvements in some cases.

See Also

• How to write conditional statements succinctly

Speed Comparison

M = rand(0:2, 10^4, 10^4);
print(first(M))

@time if first(M) == 2 && sum(M) < 1000
    print("!!")
end
@time if sum(M) < 1000 && first(M) == 2
    print("!!")
end

The only difference between the two conditionals is the order of sum(M) < 1000 and first(M) == 2, yet they perform exactly the same task. However, since first(M) == 2 merely checks if the first element of matrix M is 2, and sum(M) sums up all elements, traversing through them, the latter relatively takes longer to compute.

julia> M = rand(0:2, 10^4, 10^4);
julia> print(first(M))
0

If the first element of M is 0 as shown above, there is no need to calculate sum(M) to see if sum(M) < 1000. The speeds can vary significantly just by changing the order.

julia> @time if first(M) == 2 && sum(M) < 1000
           print("!!")
       end
  0.000009 seconds

julia> @time if sum(M) < 1000 && first(M) == 2
           print("!!")
       end
  0.040485 seconds (1 allocation: 16 bytes)

Environment

• OS: Windows
• julia: v1.7.0