[ruby-dev:26910] Re: multiplying empty string

山本です。

>|以前、[ruby-dev:19980] で話が出た時には、"" * -1 などがエラーでなくな
>|るのを気にする人がいたようです。

思いつきですが、s * -2 は s.reverse * 2 とするのはどうでしょうか。

# 数学的にも、負の掛け算は数直線上で反転を意味するのでしっくり来ます。

Index: array.c
===================================================================
RCS file: /src/ruby/array.c,v
retrieving revision 1.175
diff -u -w -b -p -r1.175 array.c
--- array.c	10 Aug 2005 01:39:24 -0000	1.175
+++ array.c	29 Aug 2005 23:59:38 -0000
@@ -2399,6 +2399,7 @@ rb_ary_times(ary, times)
 {
     VALUE ary2, tmp;
     long i, len;
+    int negative;
 
     tmp = rb_check_string_type(times);
     if (!NIL_P(tmp)) {
@@ -2406,10 +2407,9 @@ rb_ary_times(ary, times)
     }
 
     len = NUM2LONG(times);
-    if (len == 0) return ary_new(rb_obj_class(ary), 0);
-    if (len < 0) {
-	rb_raise(rb_eArgError, "negative argument");
-    }
+    if (negative = (len < 0)) len = -len;
+
+    if (len == 0 || RARRAY(ary)->len == 0) return ary_new(rb_obj_class(ary), 0);
     if (LONG_MAX/len < RARRAY(ary)->len) {
 	rb_raise(rb_eArgError, "argument too big");
     }
@@ -2421,6 +2421,7 @@ rb_ary_times(ary, times)
     for (i=0; i<len; i+=RARRAY(ary)->len) {
 	MEMCPY(RARRAY(ary2)->ptr+i, RARRAY(ary)->ptr, VALUE, RARRAY(ary)->len);
     }
+    if (negative) rb_ary_reverse_bang(ary2);
     OBJ_INFECT(ary2, ary);
 
     return ary2;
Index: string.c
===================================================================
RCS file: /src/ruby/string.c,v
retrieving revision 1.231
diff -u -w -b -p -r1.231 string.c
--- string.c	23 Jul 2005 01:02:10 -0000	1.231
+++ string.c	29 Aug 2005 23:59:47 -0000
@@ -400,6 +400,8 @@ rb_str_plus(str1, str2)
  *     "Ho! " * 3   #=> "Ho! Ho! Ho! "
  */
 
+static VALUE rb_str_reverse_bang(VALUE);
+
 VALUE
 rb_str_times(str, times)
     VALUE str;
@@ -407,12 +409,12 @@ rb_str_times(str, times)
 {
     VALUE str2;
     long i, len;
+    int negative;
 
     len = NUM2LONG(times);
-    if (len == 0) return rb_str_new5(str,0,0);
-    if (len < 0) {
-	rb_raise(rb_eArgError, "negative argument");
-    }
+    if (negative = (len < 0)) len = -len;
+
+    if (len == 0 || RSTRING(str)->len == 0) return rb_str_new5(str,0,0);
     if (LONG_MAX/len <  RSTRING(str)->len) {
 	rb_raise(rb_eArgError, "argument too big");
     }
@@ -424,6 +426,8 @@ rb_str_times(str, times)
     }
     RSTRING(str2)->ptr[RSTRING(str2)->len] = '\0';
 
+    if (negative) rb_str_reverse_bang(str2);
+
     OBJ_INFECT(str2, str);
 
     return str2;