• monarch_dodra (18/18) Oct 12 2012 I was looking in countUntil to fix another issue, and I think the
• Jonathan M Davis (13/37) Oct 12 2012 Many algorithms special case narrow strings for efficiency. However, in=
• monarch_dodra (4/42) Oct 12 2012 yeah, that's what I thought, but wanted it double checked. I'll
• =?UTF-8?B?U8O2bmtlIEx1ZHdpZw==?= (7/10) Oct 13 2012 Just wanted to mention that this kind of subtle change in behavior can

"monarch_dodra" <monarchdodra gmail.com> writes:

I was looking in countUntil to fix another issue, and I think the 
string support is broken

This program:
//----
import std.algorithm;
import std.stdio;

void main()
{
     "日本語".countUntil('本').writeln();
}
//----

Will produce "3".

...

I'd have straight up said it was a bug, but the implementation 
goes out of its way to special case narrow strings, when the 
default implementation would have produced the right result 
anyway. So I was thinking it is somehow by design...?

Am I missing something, or is it just implementation sillyness?

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Friday, October 12, 2012 21:02:47 monarch_dodra wrote:
 I was looking in countUntil to fix another issue, and I think the
 string support is broken
=20
 This program:
 //----
 import std.algorithm;
 import std.stdio;
=20
 void main()
 {
      "=E6=97=A5=E6=9C=AC=E8=AA=9E".countUntil('=E6=9C=AC').writeln();=

 }
 //----
=20
 Will produce "3".
=20
 ...
=20
 I'd have straight up said it was a bug, but the implementation
 goes out of its way to special case narrow strings, when the
 default implementation would have produced the right result
 anyway. So I was thinking it is somehow by design...?
=20
 Am I missing something, or is it just implementation sillyness?

Many algorithms special case narrow strings for efficiency. However, in=
 this=20
case, it looks just plain wrong. countUntil is supposed to return the n=
umber=20
of elements (i.e. code points in this case), but it looks like it's ret=
urning=20
the number of code units. So, I'd say that it's definitely wrong. If yo=
u want=20
code units, then use std.string.indexOf. countUntil is supposed to retu=
rn the=20
number of code points.

- Jonathan M Davis

"monarch_dodra" <monarchdodra gmail.com> writes:

On Friday, 12 October 2012 at 19:17:13 UTC, Jonathan M Davis 
wrote:
 On Friday, October 12, 2012 21:02:47 monarch_dodra wrote:
 I was looking in countUntil to fix another issue, and I think 
 the
 string support is broken
 
 This program:
 //----
 import std.algorithm;
 import std.stdio;
 
 void main()
 {
      "日本語".countUntil('本').writeln();
 }
 //----
 
 Will produce "3".
 
 ...
 
 I'd have straight up said it was a bug, but the implementation
 goes out of its way to special case narrow strings, when the
 default implementation would have produced the right result
 anyway. So I was thinking it is somehow by design...?
 
 Am I missing something, or is it just implementation sillyness?

 Many algorithms special case narrow strings for efficiency. 
 However, in this
 case, it looks just plain wrong. countUntil is supposed to 
 return the number
 of elements (i.e. code points in this case), but it looks like 
 it's returning
 the number of code units. So, I'd say that it's definitely 
 wrong. If you want
 code units, then use std.string.indexOf. countUntil is supposed 
 to return the
 number of code points.

 - Jonathan M Davis

yeah, that's what I thought, but wanted it double checked. I'll 
take care of it then.

=?UTF-8?B?U8O2bmtlIEx1ZHdpZw==?= <sludwig outerproduct.org> writes:

Am 10/12/2012 9:27 PM, schrieb monarch_dodra:
 
 yeah, that's what I thought, but wanted it double checked. I'll take
 care of it then.

Just wanted to mention that this kind of subtle change in behavior can
break a lot of code in non-obvious ways. In any case, the documentation
for countUntil, but more importantly for (last)IndexOf, needs to state
clearly what it does for narrow strings (the countUntil docs at least
imply this by using the term "elements", but an explicit statement can
do no harm).