[ExM Users] 'break' statement?

[Timothy Stitt (TGAC)]

Thanks Tim. That makes sense. I don't need it now but your example will be useful if this becomes a bigger issue later.

---

Timothy Stitt PhD / Head of Scientific Computing

The Genome Analysis Centre (TGAC)

http://www.tgac.ac.uk/


p: +44 1603 450378

e: timothy.stitt at tgac.ac.uk<mailto:timothy.stitt at tgac.ac.uk>

From: Tim Armstrong <tim.g.armstrong at gmail.com<mailto:tim.g.armstrong at gmail.com>>
Date: Tuesday, 17 March 2015 16:58
To: Timothy Stitt <timothy.stitt at tgac.ac.uk<mailto:timothy.stitt at tgac.ac.uk>>
Cc: "exm-user at lists.mcs.anl.gov<mailto:exm-user at lists.mcs.anl.gov>" <exm-user at lists.mcs.anl.gov<mailto:exm-user at lists.mcs.anl.gov>>
Subject: Re: [ExM Users] 'break' statement?

There isn't a break statement - it doesn't really fit into the language design since multiple iterations of a loop can be running at the same time.

With a foreach loop, you can't prevent iterations from running - they're all independent so there's no concept of a "next" iteration.

With the for loop, you can achieve roughly what you're talking about using the loop condition.

E.g. a contrived example where we're searching for the first odd number in an array is:

/*
 * Searching for odd numbers
 */

int A[] = [2, 4, 6, 8, 9, 11];

for (int i = 0, boolean found = false; i < size(A) && !found; i = i + 1, found = is_odd) {
  boolean is_odd = A[i] %% 2 == 1;

  if (is_odd) {
    trace(A[i]);
  }
}

This probably looks a little wonky, but with Swift sometimes you have to approach things a little differently to make them work.

I'd be a little careful trying to do some of these optimisations - there are some situations where things that work great in other languages can backfire.  The trade-off here is that if you just do a regular foreach it can start everything running entirely in parallel, rather than starting things up one at a time.  If you're not sure about something or want some ideas for how to speed up code, I'm more than happy to help.

- Tim

On 17 March 2015 at 11:32, Timothy Stitt (TGAC) <Timothy.Stitt at tgac.ac.uk<mailto:Timothy.Stitt at tgac.ac.uk>> wrote:
Hi all,

I was just wondering if there is 'break' statement in Swift 'for' and possibly 'foreach' constructs?

I have a potential use case that would benefit from this although it probably doesn't take too much overhead right now to go through the entire array looking for a particular item rather than breaking when the item is found.

Just wondered in case I missed it in the documentation.

Tim.

---

Timothy Stitt PhD / Head of Scientific Computing

The Genome Analysis Centre (TGAC)

http://www.tgac.ac.uk/


p: +44 1603 450378<tel:%2B44%201603%20450378>

e: timothy.stitt at tgac.ac.uk<mailto:timothy.stitt at tgac.ac.uk>

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