Feature #11315: [PATCH] Add Array#^ for parity with other set-like operations.

• Status: Open
• Assignee: -
• Target version: -

[0x0dea (D.E. Akers)]

Proposal

It is proposed that Array be given an "XOR" method which returns the symmetric difference between itself and another array.

Rationale

#& and #| need a friend to complete the set of set-like operations on Array.

[0x0dea (D.E. Akers)]

• File array_xor_vodka.patch array_xor_vodka.patch added

The original implementation did not correctly handle the case of repeated elements occurring an even number of times in the second array. Attached is an updated version which does not present this defect, courtesy of @apeiros and his 50-proof vodka.

[0x0dea (D.E. Akers)]

• File array_xor_recycle_seen.patch array_xor_recycle_seen.patch added

I forgot to recycle the seen hash. This last fix should finalize the patch, unless there is some very clever way to XOR two arrays without requiring two tables or a second pass through one of the arrays.

[0x0dea (D.E. Akers)]

• Tracker changed from Bug to Feature

[nobu (Nobuyoshi Nakada)]

st_update does lookup/replace/delete/insert in the callback at once.
And your patches are broken, necessary spaces are stripped.

diff --git a/array.c b/array.c
index 072e30d..737afa3 100644
--- a/array.c
+++ b/array.c
@@ -4200,6 +4200,14 @@ rb_ary_or(VALUE ary1, VALUE ary2)
     return ary3;
 }
 
+static int
+ary_hash_xorset(st_data_t *key, st_data_t *value, st_data_t arg, int existing)
+{
+    if (existing) return ST_DELETE;
+    *key = *value = (VALUE)arg;
+    return ST_CONTINUE;
+}
+
 /*
  *  call-seq:
  *     ary ^ other_ary     -> new_ary
@@ -4228,15 +4236,9 @@ rb_ary_xor(VALUE ary1, VALUE ary2)
     result = ary_make_hash(ary1);
 
     for (i = 0; i < RARRAY_LEN(ary2); ++i) {
-    elt = (st_data_t)RARRAY_AREF(ary2, i);
-    if (st_lookup(RHASH_TBL_RAW(seen), elt, 0)) continue;
-    st_update(RHASH_TBL_RAW(seen), elt, ary_hash_orset, elt);
-    if (st_lookup(RHASH_TBL_RAW(result), elt, 0)) {
-        st_delete(RHASH_TBL_RAW(result), &elt, 0);
-    }
-    else {
-        st_update(RHASH_TBL_RAW(result), elt, ary_hash_orset, elt);
-    }
+	elt = (st_data_t)RARRAY_AREF(ary2, i);
+	if (!st_update(RHASH_TBL_RAW(seen), elt, ary_hash_orset, elt))
+	    st_update(RHASH_TBL_RAW(result), elt, ary_hash_xorset, elt);
     }
 
     ary3 = rb_hash_values(result);