From: Vincent Isambart <vincent.isambart@...>
Date: 2008-01-21T02:02:28+09:00
Subject: [ruby-dev:33222] Re: Ruby1.9String   	　バイト列へのインデックス　アクセス

バンサンです。

On Jan 20, 2008, at 12:44 PM, Vincent Isambart wrote:

> これはどうでしょうか：
> s = 'a'
> s.bytes[0] # => 97
> s.bytes[0] = 98
> s # => 'b'
> s.bytes[0] = 'c' # 'c'の長さが1バイトじゃなかったら例 
> 外を発生
> s # => 'c'


概念実証のため、作ってみました。
注意：実装はひどい（特にEnumeratorからStringを読 
み込む方法）しRangeも対応できないです（実はRange 
を受けるべきかどうかはわかりません）。

Index: string.c
===================================================================
--- string.c	(revision 15145)
+++ string.c	(working copy)
@@ -4521,7 +4521,80 @@
      return str;
  }

+struct enumerator {
+    VALUE method;
+    VALUE proc;
+    VALUE args;
+    rb_block_call_func *iter;
+    VALUE fib;
+    VALUE dst;
+    VALUE no_next;
+};

+static VALUE
+rb_str_bytes_aref(VALUE obj, VALUE indx)
+{
+    long idx, len;
+    struct enumerator *ptr;
+    VALUE str;
+
+    Data_Get_Struct(obj, struct enumerator, ptr);
+
+    str = rb_funcall(ptr->method, rb_intern("receiver"), 0);
+
+    idx = FIX2LONG(indx);
+    len = RSTRING_LEN(str);
+    if (idx < 0)
+	idx += len;
+
+    if ((idx < 0) || (idx >= len))
+	return Qnil;
+
+    return INT2FIX(RSTRING_PTR(str)[idx] & 0xff);
+}
+
+static VALUE
+rb_str_bytes_aset(VALUE obj, VALUE indx, VALUE val)
+{
+    long idx, len, v;
+    struct enumerator *ptr;
+    VALUE str;
+
+    Data_Get_Struct(obj, struct enumerator, ptr);
+
+    str = rb_funcall(ptr->method, rb_intern("receiver"), 0);
+
+    idx = FIX2LONG(indx);
+    len = RSTRING_LEN(str);
+    if (idx < 0)
+	idx += len;
+
+    if ((idx < 0) || (idx >= len))
+	rb_raise(rb_eIndexError, "index %ld out of string", FIX2LONG(indx));
+
+    switch (TYPE(val)) {
+      case T_FIXNUM:
+	v = FIX2LONG(val);
+	RSTRING_PTR(str)[idx] = (v & 0xff);
+	break;
+
+      case T_STRING:
+	if (RSTRING_LEN(val) != 1) {
+	    rb_raise(rb_eTypeError,
+		     "type mismatch: the string must be one byte long",
+		     rb_obj_classname(val));
+	}
+	RSTRING_PTR(str)[idx] = RSTRING_PTR(val)[0];
+	break;
+
+      default:
+	rb_raise(rb_eTypeError, "type mismatch: %s given",
+		 rb_obj_classname(val));
+    }
+
+    return val;
+}
+
  /*
   *  Document-method: bytes
   *  call-seq:
@@ -4553,7 +4626,14 @@
  {
      long i;

-    RETURN_ENUMERATOR(str, 0, 0);
+    if (!rb_block_given_p()) {
+	VALUE enumerator;
+	
+	enumerator = rb_enumeratorize(str, ID2SYM(rb_frame_this_func()), 0,  
0);
+	rb_define_singleton_method(enumerator, "[]", rb_str_bytes_aref, 1);
+	rb_define_singleton_method(enumerator, "[]=", rb_str_bytes_aset, 2);
+	return enumerator;
+    }
      for (i=0; i<RSTRING_LEN(str); i++) {
  	rb_yield(INT2FIX(RSTRING_PTR(str)[i] & 0xff));
      }