2 more use cases:
1) When writing a deep recursion
Throwing an exception will directly jump to your "catch" block without having to unfold every return call site on the stack one by one. Which can be much faster if the recursion is very "deep".
2) When your exception is exceptional :-)
If Not_found is never caught, then using exceptions is faster than option because you don't have to allocate to perform the "find" operation (the difference should be minimal though).
Plus it makes your code more readable, you don't have to match on the return value of the find.
This use case makes sense if you don't intend to catch Not_found, when Not_found is a bug, period.
Le 4 avril 2012 13:38, John Carr
<jfc@mit.edu> a écrit :
When thinking about performance, consider the "try" keyword to take time
to execute. A try block pushes an exception handler onto a stack and
pops the stack on exit. The try block may also interfere with tail call
optimizations.
A loop like
for i = 0 to 10000000 do try ... done
executes "try" 10000001 times and will run much more slowly than
try for i = 0 to 10000000 do ... done
where "try" only executes once.
I use options where performance matters, in frequently executed code
where the amount of computation is not much more than the overhead of
a try...with. For example, I have variants of List.assoc that return
options instead of raising exceptions.
Where performance doesn't matter, i.e. the amount of code in the block
is large or the block is rarely executed, I use exceptions or options
based on convenience.
> I benchmarked two programs, in one case the main function throw an exception
> that is caught, in the other the function returns an option that is pattern
> matched on.
>
> I noticed that, whether the exception is thrown or not, the option version is
> always faster.
>
> Is there any case where it makes sense, performance wise, to use exception
> instead of 'a option ?
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