On 13 February 2014, Bram Moolenaar <[email protected]> wrote:
>
> lcd wrote:
>
> > There is an asymmetry in handling indices for lists and strings.
> > Lists accept things like lst[n], lst[n1:n2], lst[n1:-n2], and lst[-n].
> > Strings accept str[n], str[n1:n2], str[n1:-n2] (all with the same
> > meanings as the corresponding operations for lists), but not str[-n].
> > Negative indices in strings always return '', which is frustrating. :)
> >
> > The patch below makes negative indices behave the same way for
> > string as they do for lists (but they don't rise exceptions when out of
> > range):
> >
> > :let a = '12345'
> > :echo a[-1]
> > 5
> > :echo string(a[-6])
> > ''
> >
> > Negative indices for strings never did anything useful (at least as
> > far as I can tell), so this is unlikely to break existing code.
>
> I suppose that would be OK, and useful, to add.
>
> Can you also add a test?
Sure, attached below.
/lcd
diff -r 277885c9c344 src/eval.c
--- a/src/eval.c Wed Feb 12 22:08:49 2014 +0100
+++ b/src/eval.c Fri Feb 14 09:38:11 2014 +0200
@@ -5414,8 +5414,10 @@
else
{
/* The resulting variable is a string of a single
- * character. If the index is too big or negative the
+ * character. If the index is out of range the
* result is empty. */
+ if (n1 < 0)
+ n1 = len + n1;
if (n1 >= len || n1 < 0)
s = NULL;
else
diff -r 277885c9c344 src/testdir/Makefile
--- a/src/testdir/Makefile Wed Feb 12 22:08:49 2014 +0100
+++ b/src/testdir/Makefile Fri Feb 14 09:38:11 2014 +0200
@@ -31,7 +31,7 @@
test89.out test90.out test91.out test92.out test93.out \
test94.out test95.out test96.out test97.out test98.out \
test99.out test100.out test101.out test102.out test103.out \
- test104.out
+ test104.out test105.out
SCRIPTS_GUI = test16.out
diff -r 277885c9c344 src/testdir/test105.in
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/testdir/test105.in Fri Feb 14 09:38:11 2014 +0200
@@ -0,0 +1,12 @@
+Tests negative indices in strings
+
+STARTTEST
+:let a='12345'
+:for i in range(1, 6)
+: $put =string(a[-i])
+:endfor
+:/^Results/,$wq! test.out
+:qa!
+ENDTEST
+
+Results:
diff -r 277885c9c344 src/testdir/test105.ok
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/testdir/test105.ok Fri Feb 14 09:38:11 2014 +0200
@@ -0,0 +1,7 @@
+Results:
+'5'
+'4'
+'3'
+'2'
+'1'
+''
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