=begin
なかだです。

ブロックの値にしたがって一意のものを選ぶ、Array#uniq_byというの
はどうでしょうか。

Index: array.c

--- array.c (revision 22100)
+++ array.c (working copy)
@@ -2875,13 +2875,40 @@ ary_add_hash(VALUE hash, VALUE ary)
}

-static VALUE
-ary_make_hash(VALUE ary)
+static inline VALUE
+ary_tmp_hash_new(void)
{
VALUE hash = rb_hash_new();

  RBASIC(hash)->klass = 0;

• return hash;
  +}

+static VALUE
+ary_make_hash(VALUE ary)
+{

• VALUE hash = ary_tmp_hash_new();
  return ary_add_hash(hash, ary);
  }

+static VALUE
+ary_add_hash_by(VALUE hash, VALUE ary)
+{

• long i;
• for (i = 0; i < RARRAY_LEN(ary); ++i) {
• VALUE v = rb_ary_elt(ary, i), k = rb_yield(v);
• if (rb_hash_lookup2(hash, k, Qundef) == Qundef) {

•  rb_hash_aset(hash, k, v);
  

• }
• }
• return hash;
  +}

+static VALUE
+ary_make_hash_by(VALUE ary)
+{

• VALUE hash = ary_tmp_hash_new();
• return ary_add_hash_by(hash, ary);
  +}

static inline void
ary_recycle_hash(VALUE hash)
@@ -3063,4 +3090,43 @@ rb_ary_uniq(VALUE ary)
}

+static int
+push_value(st_data_t key, st_data_t val, st_data_t ary)
+{

• rb_ary_push((VALUE)ary, (VALUE)val);
• return ST_DELETE;
  +}

+static VALUE
+rb_ary_uniq_by_bang(VALUE ary)
+{

• VALUE hash;
• long size;
• RETURN_ENUMERATOR(ary, 0, 0);
• hash = ary_make_hash_by(ary);
• size = RHASH_SIZE(hash);
• if (RARRAY_LEN(ary) == size) return Qnil;
• ary_resize_capa(ary, size);
• ARY_SET_LEN(ary, 0);
• st_foreach(RHASH_TBL(hash), push_value, ary);
• ary_recycle_hash(hash);
• return ary;
  +}

+static VALUE
+rb_ary_uniq_by(VALUE ary)
+{

• VALUE hash;
• long size;
• RETURN_ENUMERATOR(ary, 0, 0);
• hash = ary_make_hash_by(ary);
• size = RHASH_SIZE(hash);
• ary = ary_new(rb_obj_class(ary), size);
• st_foreach(RHASH_TBL(hash), push_value, ary);
• ary_recycle_hash(hash);
• return ary;
  +}

/*

• call-seq:
  @@ -3920,4 +3986,6 @@ Init_Array(void)
  rb_define_method(rb_cArray, "uniq", rb_ary_uniq, 0);
  rb_define_method(rb_cArray, "uniq!", rb_ary_uniq_bang, 0);

• rb_define_method(rb_cArray, "uniq_by", rb_ary_uniq_by, 0);
• rb_define_method(rb_cArray, "uniq_by!", rb_ary_uniq_by_bang, 0);
  rb_define_method(rb_cArray, "compact", rb_ary_compact, 0);
  rb_define_method(rb_cArray, "compact!", rb_ary_compact_bang, 0);
  Index: enum.c
  ===================================================================
  --- enum.c (revision 22100)
  +++ enum.c (working copy)
  @@ -1794,4 +1794,29 @@ enum_cycle(int argc, VALUE *argv, VALUE
  }

+static VALUE
+enum_uniq_by_i(VALUE i, VALUE hash, int argc, VALUE *argv)
+{

• return rb_hash_aset(hash, rb_yield_values(argc, argv), i);
  +}

+static int
+push_value(st_data_t key, st_data_t val, st_data_t ary)
+{

• rb_ary_push((VALUE)ary, (VALUE)val);
• return ST_DELETE;
  +}

+static VALUE
+enum_uniq_by(VALUE obj)
+{

• VALUE hash = rb_hash_new(), uniq;
• RBASIC(hash)->klass = 0;
• rb_block_call(obj, id_each, 0, 0, enum_uniq_by_i, hash);
• uniq = rb_ary_new2(RHASH_SIZE(hash));
• st_foreach(RHASH_TBL(hash), push_value, uniq);
• return uniq;
  +}

/*

• The Enumerable mixin provides collection classes with
  @@ -1853,4 +1878,5 @@ Init_Enumerable(void)
  rb_define_method(rb_mEnumerable, "drop_while", enum_drop_while, 0);
  rb_define_method(rb_mEnumerable, "cycle", enum_cycle, -1);

• rb_define_method(rb_mEnumerable, "uniq_by", enum_uniq_by, 0);

  id_eqq = rb_intern("===");
  

--
--- 僕の前にBugはない。
--- 僕の後ろにBugはできる。
中田 伸悦
=end