snax

inline rescue vs. respond_to? cage fight

Which is faster? Inline rescue, or classic branching based on the respond_to? method? Let’s face them off.

ding

Download this, then run like so:

$ ruby test_rescue.rb success respond_to
0.947819 seconds
$ ruby test_rescue.rb success rescue
0.575646 seconds
$ ruby test_rescue.rb failure respond_to
0.789487 seconds
$ ruby test_rescue.rb failure rescue
16.1751 seconds

This suggests that a clean rescue path is about twice as fast as a successful respond_to? condition. But a raised rescue is 20 times slower than a failed respond_to?.

a champion! sort of

Excusing my slipshod math and neglect of all other relevant factors, this means that in time-critical code paths we should use respond_to? unless the path is predicted to fail less than 2.5% of the time. So it depends.