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IDProjectCategoryView StatusLast Update
0000260LDMudLPC Compiler/Preprocessorpublic2009-10-01 05:21
ReporterlarsAssigned To 
Status newResolutionopen 
Summary0000260: Make '>' indexing default, with an option?
DescriptionShort: Make > indexing default with an option ?
From: Tomba@Batmud
Date: 2001-08-25
Type: Feature
State: New

Anyway, I was wondering what's the difference between normal indexing and
> indexing. Isn't normal indexing just a subset of > indexing? If so, why
not default to > style indexing and add a compile time option for allowing
or disabling negative indexes. Just to clear up a bit, arr[-2] would be
the same as arr[>-2] etc.

Batmud's old driver works this way, and even if I have already made my own
changes to ldmud to allow negative indexing, it'd be nice to have it by
default. =)

And Alfe said to this topic:

Alfe says: man koennte vielleicht folgendes sagen:
Alfe says: x[>a..>b] ist das, was x[a..b] bisher ist.
Alfe says: x[a..b] ist das, was extract(x,a,b) bisher ist (d.h. vorzeichen
  legt fest, ob von rechts oder links).
Alfe says: und x[<a..<b] ist wie gehabt.

Alfe says: aber dann muesste man mal durchs mud gehen und alle vorkommen von
  x[a..b] ueberpruefen
Alfe says: du kannst nicht garantieren, dass ein x[a..b] bisher immer mit
  positiven werten arbeitete, also solltest du besser davon ausgehen, dass
  alle stellen potentiell auch mit negativen werten passieren koennen.
Alfe says: demnach stehe ich dieser version etwas ambivalent gegenueber.
Alfe says: es waere zwar sehr schoen, wenn das < sagt: von rechts, das > sagt:
  von links und sonst sagt das vorzeichen das.
Alfe says: denn das ist logisch strukturiert.

Alfe says: so gesehen waere es vielleicht besser, wenn das x[>a..>b]
  bedeutet, dass das vorzeichen entscheidet und x[a..b] wie gehabt bleibt.
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2009-09-30 17:25

administrator   ~0001373

Just until now I thought, that indexing with negative numbers/ranges is deprecated but I seem to be wrong.
Can anybody tell me about the real purpose of indexing something from before the beginning?


2009-09-30 17:33

manager   ~0001375

Single indices (a[x]) are not allowed to be negative, but indices in ranges can be (a[-1..x] is the same as a[0..x]). Ranges are much sloppier than normal indexing operations.


2009-09-30 17:37

administrator   ~0001376

Mhmm, is it feasible to deprecate negative numbers in ranges and issue warnings and errors with pedantic (and later even without). Or is that too heavily used?


2009-09-30 17:44

manager   ~0001378

Can't say without warnings... (With the deprecated indexing past string ends we got more warnings than I expected, so there might be a lot of that around, too.)


2009-10-01 05:08

updater   ~0001390

One the one hand, as long as the driver ensures all ranges that start below 0 to be remapped to 0..rangemax I would rather call it a feature than a bug. It allows for a very easy-to-use way to get that last n elements (or less if there are less than n elements at all) of an array/string.
On the other hand, this possibility implies, that I should also be able to get the first n elements of an array/string by [0..(n-1)] - which might complain about indexing past string end.

So, for the sake of consistency, I would opt for deprecating negative indices.


2009-10-01 05:21

administrator   ~0001391

Ok, but that is possible without negative indices:
[0..n-1]: first n elements
[<n..]: last n elements

This negative indices I meant was [-3..-1] which is the empty array/string and [-2..2] which is [0..2]. I don't really think, you need the negative indices as they are now (for other than backwards compatibility).
Something else would be to use the sign instead of <. That [-3..] would be the last 3 elements, but to change to this will silently break code and I would not like that.

Issue History

Date Modified Username Field Change
2004-11-27 00:11 lars New Issue
2009-09-30 17:25 zesstra Note Added: 0001373
2009-09-30 17:33 Gnomi Note Added: 0001375
2009-09-30 17:37 zesstra Note Added: 0001376
2009-09-30 17:44 Gnomi Note Added: 0001378
2009-10-01 05:08 Sorcerer Note Added: 0001390
2009-10-01 05:21 zesstra Note Added: 0001391