On Sat, May 17, 2014 at 9:59 PM, Hans W Borchers <[email protected]> wrote:
> Yesterday I implemented a function calculating arc length of curves (to the
> last digit) when I came across the following stumbling blocks. Image the
> following function where I leave a for-loop with a 'break' statement:
>
> function testfun1(x::Vector{Float64})
> for i = 1:length(x)
> if x[i] == 0.0
> break
> end
> end
> return i-1
> end
For this particular example, I'd suggest you just return i-1 directly
inside the loop:
function testfun1(x::Vector{Float64})
for i = 1:length(x)
if x[i] == 0.0
return i-1
end
end
return length(x)-1 # Or other special case for when 0 isn't found
end
Using an early return like this is really quite powerful, especially when
you have a deeply nested set of loops. I use it all the time in C++.
> I understand that the scope of the loop variable is restricted to the loop
> itself. What is the best way to "export" i to the outside? For the moment
> I settled with defining i before the loop.
Yes, if you want i accessible outside a loop, you'll just have to declare
it in the outer scope. AFAIK you've done the right thing there, though
initializing i to a default would be more concise and wouldn't fail if the
input array is empty (unless that's intentional).
> This works, but I must admit it runs against my gut feeling and
> experience with other scientific programming languages.
It's true that the looser scoping rules of langauges like matlab and python
can be convenient. On the whole I prefer tighter scoping rules like C++
though: they make code easier to reason about by making the data
flow more local.
~Chris
