# Bug in Array#slice!

**URL:** <https://www.ruby-forum.com/t/bug-in-array-slice/122650>\
**Category:** Development\
**Created:** [December 10, 2007, 11:28am UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650 "2007-12-10T11:28:14Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 11:28am UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/1 "2007-12-10T11:28:14Z")

</div>

e$BCf@n$H$$$$$^$9!#e(B

[ruby-dev:31761] e$B$G0lEY%l%]!\<%H$7$?$N$G$9$,!“e(BArray e$B$N4pe(B  
e$BK\E\*$J$H$3$m$N%P%0$G=EMW$@$H;W$o$l$k$N$G!”$b$&0lEY\>$7$/%le(B  
e$B%]!\<%H$7$^$9!#e(B

Array#slice! e$B$G!"Ii$NHO0O30$Ne(B index e$B$r;XDj$7$?\>l9g!“Nce(B  
e$B30$K$J$i$J$$$3$H$,$”$j$^$9!#e(B  
trunk e$B$He(B 1.8 e$B$G:F8=$7$^$9!#e(B

e$B6qBNE\*$K$O!"e(B

$ ./ruby -e ‘a = %w|a b c d e|; a.slice!(-3,2); p a’  
[“a”, “b”, “e”]

$ ./ruby -e ‘a = %w|a b c d e|; a.slice!(-8,2); p a’  
[“a”, “b”, “e”]

e$B$N$h$&$J\>l9g$G$9!#e(B  
e$B$3$N\>l9g!"e(B-3 e$B$He(B -8 e$B$,F10l;k$5$l$F$7$^$C$F$$$^$9!#e(B

$ ./ruby -e ‘a = %w|a b c d e|; a.slice!(-13,2); p a’  
-e:1:in `slice!': index -8 out of array (IndexError) from -e:1:in`’

e$B$?$a$7$Ke(B -13 e$B$r;XDj$9$k$H!“e(Bindex -8 e$B$OHO0O30$@$He(B  
e$B$$$&%(%i!\<$K$J$k$N$G!”$I$3$+$Ge(B Array#size e$B$r8m$C$FB-$7e(B  
e$B$F$7$^$C$F$$$k$3$H$,$o$+$j$^$9!#e(B

e$B%=!\<%9$r8+$k$H!“e(Brb\_ary\_slice\_bang e$B\<+BN$H!”$=$3$+$i8F$s$G$$e(B  
e$B$ke(B rb\_ary\_splice e$B$Ge(B2e$BEYB-$79~$s$G$7$^$C$F$$$k$h$&$G$9!#e(B

e$B0J2\<$N%Q%C%A$G!"e(B

$ ./ruby -e ‘a = %w|a b c d e|; a.slice!(-3,2); p a’  
[“a”, “b”, “e”]

$ ./ruby -e ‘a = %w|a b c d e|; a.slice!(-8,2); p a’  
-e:1:in `slice!': index -8 out of array (IndexError) from -e:1:in`’

e$B$H@5$7$/F0:n$9$k$3$H$r3NG’$7$^$7$?!#e(B

# Index: array.c

— array.c (revision 14178)  
+++ array.c (working copy)  
@@ -1886,9 +1886,6 @@  
pos = NUM2LONG(arg1);  
len = NUM2LONG(arg2);  
delete\_pos\_len:

- if (pos \< 0) {
- 

```
 pos = RARRAY_LEN(ary) + pos;

```

- }  
arg2 = rb\_ary\_subseq(ary, pos, len);  
rb\_ary\_splice(ary, pos, len, Qundef); /\* Qnil/rb\_ary\_new2(0) \*/  
return arg2;

---

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 12:18pm UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/2 "2007-12-10T12:18:11Z")

</div>

At Mon, 10 Dec 2007 19:27:17 +0900,  
Satoshi N. wrote:

> [ruby-dev:31761] で一度レポートしたのですが、Array の基 本的なところの  
> バグで重要だと思われるので、もう一度詳しくレ ポートします。

　これは [ruby-dev:31671] ですかね。見落とされている…。

> Array#slice! ã§ã€è² ã®ç¯„å›²å¤–ã® index ã‚’æŒ‡å®šã—ãŸå ´åˆã€ä¾‹ 外にならないこと  
> があります。  
> trunk と 1.8 で再現します。

　Array#slice と挙動を合わせるべきだと思うので、ここは例外を  
上げずに nil を返しましょうか。

# Index: array.c

— array.c (revision 14180)  
+++ array.c (working copy)  
@@ -1963,6 +1963,7 @@  
delete\_pos\_len:  
if (pos \< 0) {  
pos = RARRAY(ary)-\>len + pos;

- 

```
 if (pos < 0) return Qnil;

```

}  
arg2 = rb\_ary\_subseq(ary, pos, len);  
rb\_ary\_splice(ary, pos, len, Qnil); /\* Qnil/rb\_ary\_new2(0) \*/

–  
/  
/\_\_ \_\_ [Akinori.org](http://Akinori.org) / [MUSHA.org](http://MUSHA.org)  
/ ) ) ) ) / [FreeBSD.org](http://FreeBSD.org) / [Ruby-lang.org](http://Ruby-lang.org)  
Akinori MUSHA aka / (\_ / ( (\_\_( @ [iDaemons.org](http://iDaemons.org) / and.or.jp

“Different eyes see different things,  
Different hearts beat on different strings –  
But there are times for you and me when all such things agree”

---

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 12:51pm UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/3 "2007-12-10T12:51:04Z")

</div>

On 2007/12/10, at 20:17, Akinori MUSHA wrote:

> e$B!!$3$l$Oe(B [ruby-dev:31671] e$B$G$9$+$M!#8+Mn$H$5$l$F$$$k!D!#e(B

e$B$9$\_$^$;$s!#$=$NDL$j$G$7$?!#e(B

> e$B!!e(BArray#slice e$B$H5sF0$r9g$o$;$k$Y$-$@$H;W$&$N$G!"$3$3e(B  
> e$B$ONc30$re(B  
> e$B\>e$2$:$Ke(B nil e$B$rJV$7$^$7$g$&$+!#e(B

e$B3N$+$K$=$A$i$N$[$&$,$$$$$H;W$$$^$9!#e(B  
Array#slice! e$B$G@5$NHO0O30$r;XDj$7$?\>l9g$H!"e(BString#slice!  
e$B$G@5Ii$NHO0O30$r;XDj$7$?\>l9g$r8+$k$He(B nil e$B$rJV$7$F$$$k$N$G!#e(B

$ ./ruby -e ‘a = %w|a b c d e|; p a.slice!(8,2); p a’  
nil  
[“a”, “b”, “c”, “d”, “e”, nil, nil, nil]

$ ./ruby -e ‘s = “abcde”; p s.slice!(8,2); p s’  
nil  
“abcde”  
$ ./ruby -e ‘s = “abcde”; p s.slice!(-8,2); p s’  
nil  
“abcde”

---

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 1:42pm UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/4 "2007-12-10T13:42:11Z")

</div>

e$B$^$D$b$He(B e$B$f$-$R$m$G$9e(B

In message “Re: [ruby-dev:32519] Re: bug in Array#slice!”  
on Mon, 10 Dec 2007 20:17:20 +0900, “Akinori MUSHA”  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:  
|  
|[1 \<text/plain; ISO-2022-JP (7bit)\>]  
|At Mon, 10 Dec 2007 19:27:17 +0900,  
|Satoshi N. wrote:  
|\> [ruby-dev:31761] e$B$G0lEY%l%]!\<%H$7$?$N$G$9$,!“e(BArray e$B$N4pe(B e$BK\E\*$J$H$3$m$Ne(B  
|\> e$B%P%0$G=EMW$@$H;W$o$l$k$N$G!”$b$&0lEY\>$7$/%le(B e$B%]!\<%H$7$^$9!#e(B  
|  
|e$B!!$3$l$Oe(B [ruby-dev:31671] e$B$G$9$+$M!#8+Mn$H$5$l$F$$$k!D!#e(B

e$B$=$&$\_$?$$$G$9!#$4$a$s$J$5$$!#e(B

|\> Array#slice! e$B$G!“Ii$NHO0O30$Ne(B index e$B$r;XDj$7$?\>l9g!“Nce(B e$B30$K$J$i$J$$$3$He(B  
|\> e$B$,$”$j$^$9!#e(B  
|\> trunk e$B$He(B 1.8 e$B$G:F8=$7$^$9!#e(B  
|  
|e$B!!e(BArray#slice e$B$H5sF0$r9g$o$;$k$Y$-$@$H;W$&$N$G!”$3$3$ONc30$re(B  
|e$B\>e$2$:$Ke(B nil e$B$rJV$7$^$7$g$&$+!#e(B

1.8e$B$K%3%\_%C%H$7$F$/$@$5$$!#e(Btrunke$B$O;d$,$d$j$^$9!#e(B

---

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 1:46pm UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/5 "2007-12-10T13:46:53Z")

</div>

At Mon, 10 Dec 2007 20:59:56 +0900,  
matz wrote:

> |At Mon, 10 Dec 2007 19:27:17 +0900,  
> |Satoshi N. wrote:  
> |\> [ruby-dev:31761] で一度レポートしたのですが、Array の基 本的なところの  
> |\> バグで重要だと思われるので、もう一度詳しくレ ポートします。  
> |  
> |　これは [ruby-dev:31671] ですかね。見落とされている…。
> 
> そうみたいです。ごめんなさい。

　僕もです。1.8 も該当するし、 Array#slice! という名前を提案した  
のは自分だった気がするので、見落としたのは痛恨です。

> |\> Array#slice! ã§ã€è² ã®ç¯„å›²å¤–ã® index ã‚’æŒ‡å®šã—ãŸå ´åˆã€ä¾‹ 外にならないこと  
> |\> があります。  
> |\> trunk と 1.8 で再現します。  
> |  
> |　Array#slice と挙動を合わせるべきだと思うので、ここは例外を  
> |上げずに nil を返しましょうか。
> 
> 1.8にコミットしてください。trunkは私がやります。

　あ、修正は同じなので一緒にやろうと思いましたが、分かりました。  
よろしくお願いします。

ã€€ãƒ†ã‚¹ãƒˆã‚±ãƒ¼ã‚¹ã‚’è¿½åŠ ã—ã¦ãŠãã¾ã™ã€‚

–  
/  
/\_\_ \_\_ [Akinori.org](http://Akinori.org) / [MUSHA.org](http://MUSHA.org)  
/ ) ) ) ) / [FreeBSD.org](http://FreeBSD.org) / [Ruby-lang.org](http://Ruby-lang.org)  
Akinori MUSHA aka / (\_ / ( (\_\_( @ [iDaemons.org](http://iDaemons.org) / and.or.jp

“Different eyes see different things,  
Different hearts beat on different strings –  
But there are times for you and me when all such things agree”

---

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 2:55pm UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/6 "2007-12-10T14:55:43Z")

</div>

e$B$^$D$b$He(B e$B$f$-$R$m$G$9e(B

In message “Re: [ruby-dev:32528] Re: bug in Array#slice!”  
on Mon, 10 Dec 2007 22:28:50 +0900, “Akinori MUSHA”  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

|e$B!!@h$N=$@5$@$1$@$He(B Range e$B$rEO$7$?\>l9g$Ke(B rb\_range\_beg\_len() e$B$Ke(B  
|e$BNc30$r=P$5$l$F$7$^$&$N$G!"$=$A$i$bBP=h$7$^$7$?!#e(B  
|  
|\> e$B!!%F%9%H%1!\<%9$rDI2C$7$F$_$-$^$9!#e(B  
|  
|e$B!!e(Btest\_array.rb e$B$K$$$/$D$+F~$l$F$_$-$^$7$?!#e(B

e$B$\*\<j?t$+$1$^$7$?!#$"$j$,$H$&$4$6$$$^$9!#e(B

---

<div class="post-metadata">

**Author:** ![Satoshi\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/6de8d8/32.png) [@Satoshi\_N](https://www.ruby-forum.com/u/Satoshi_N)\
**Post date:** [December 10, 2007, 2:29pm UTC](https://www.ruby-forum.com/t/bug-in-array-slice/122650/7 "2007-12-10T14:29:49Z")

</div>

At Mon, 10 Dec 2007 21:16:51 +0900,  
I wrote:

> よろしくお願いします。  
> 　先の修正だけだと Range ã‚’æ¸¡ã—ãŸå ´åˆã« rb\_range\_beg\_len() に  
> 例外を出されてしまうので、そちらも対処しました。

> ã€€ãƒ†ã‚¹ãƒˆã‚±ãƒ¼ã‚¹ã‚’è¿½åŠ ã—ã¦ãŠãã¾ã™ã€‚

　test\_array.rb にいくつか入れておきました。

　あとで 1.8 にも入れます。

–  
/  
/\_\_ \_\_ [Akinori.org](http://Akinori.org) / [MUSHA.org](http://MUSHA.org)  
/ ) ) ) ) / [FreeBSD.org](http://FreeBSD.org) / [Ruby-lang.org](http://Ruby-lang.org)  
Akinori MUSHA aka / (\_ / ( (\_\_( @ [iDaemons.org](http://iDaemons.org) / and.or.jp

“Different eyes see different things,  
Different hearts beat on different strings –  
But there are times for you and me when all such things agree”