Re^2: Untillian Headache or about the semantic of until

Oddly enough, the $wheel < 0 may be unnecessary even if it does aid in clarification.

Only in the case of the odometer 'turning over' will $wheel go negative. When $wheel is -1, $odometer[ $wheel ] will be the same as $odometer[ $#odometer ], which will have already been set to 0.

... of course relying on this in your code will piss off your maintainers.

TJD

Comment on Re^2: Untillian Headache or about the semantic of until Select or Download Code

Replies are listed 'Best First'.
Re^3: Untillian Headache or about the semantic of until by BrowserUk (Patriarch) on Feb 12, 2013 at 22:38 UTC
Oddly enough, the $wheel < 0 may be unnecessary Indeed. When I originally posted my suggestion, it was purely on the basis of reading the code snippet in the OP. In general, when doing this kind of iteration with a while loop, I check the range of the index before attempting to use it to access the array. Only after discipulus refuted the idea, did I download the snippet and play with it and found that as posted, it "worked okay". It took a little more investigation to understand that it gets away with it because of perl's propensity to accept negative array indices. The funny thing is, that in one way, coding it "wrongly" has a benefit: <Reveal this spoiler or all in this thread> Coded 'correctly' attempts to iterate beyond the scale of the odometer fail silently: `1 2 3 ... 97 98 99` [download] But coded 'wrongly', that beyond range attempt fails noisely: `1 2 3 ... 98 99 Use of uninitialized value within @odo in numeric lt (<) at C:\test\ju +nk31.pl line 9. Use of uninitialized value within @odo in numeric lt (<) at C:\test\ju +nk31.pl line 9.` [download] which could be seen as an advantage :) Of course, there are better ways of detecting the failure... With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^3: Untillian Headache or about the semantic of until
by BrowserUk (Patriarch) on Feb 12, 2013 at 22:38 UTC

Oddly enough, the $wheel < 0 may be unnecessary

Indeed.

When I originally posted my suggestion, it was purely on the basis of reading the code snippet in the OP. In general, when doing this kind of iteration with a while loop, I check the range of the index before attempting to use it to access the array.

Only after discipulus refuted the idea, did I download the snippet and play with it and found that as posted, it "worked okay".

It took a little more investigation to understand that it gets away with it because of perl's propensity to accept negative array indices.

The funny thing is, that in one way, coding it "wrongly" has a benefit:

Coded 'correctly' attempts to iterate beyond the scale of the odometer fail silently:
```
1
2
3
...
97
98
99
[download]
```

But coded 'wrongly', that beyond range attempt fails noisely:

1
2
3
...
98
99

Use of uninitialized value within @odo in numeric lt (<) at C:\test\ju
+nk31.pl line 9.

Use of uninitialized value within @odo in numeric lt (<) at C:\test\ju
+nk31.pl line 9.
[download]

which could be seen as an advantage :)

Of course, there are better ways of detecting the failure...

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

[reply]
[d/l]
[select]