Add additional query functions to Traversable<G>

* one_match (Predicate<G>) check if exactly one element matches
* count_match (Predicate<G>) returns the count of items that matches

https://bugzilla.gnome.org/show_bug.cgi?id=781641

2 files changed, 83 insertions, 0 deletions

diff --git a/gee/traversable.vala b/gee/traversable.vala
index 9383041..3745f08 100644
--- a/gee/traversable.vala
+++ b/gee/traversable.vala
@@ -558,6 +558,45 @@ public interface Gee.Traversable<G> : Object {
 		return result.iterator ();
 	}
 
+	/**
+	 * Checks if a signle element matches the given predicate.
+	 *
+	 * @param pred Predicate to be called to check for matches
+	 * @return If a single element matches the predicate
+	 * @since 0.20.1
+	 */
+	[CCode (ordering = 16)]
+	public virtual bool one_match (owned Predicate<G> pred) {
+		int count = 0;
+		this.foreach ((item) => {
+			if (pred (item)) {
+				count++;
+				return count <= 1;
+			}
+			return true;
+		});
+		return count == 1;
+	}
+
+	/**
+	 * Counts the number of elements matching the given predicate.
+	 *
+	 * @param pred Predicate to be called to check for matches
+	 * @return The number of elements matching the pre
+	 * @since 0.20.1
+	 */
+	[CCode (ordering = 17)]
+	public virtual int count_match (owned Predicate<G> pred) {
+		int count = 0;
+		this.foreach ((item) => {
+			if (pred (item)) {
+				count++;
+			}
+			return true;
+		});
+		return count;
+	}
+
 	public enum Stream {
 		YIELD,
 		CONTINUE,
diff --git a/tests/testcollection.vala b/tests/testcollection.vala
index 819e130..0a2b40a 100644
--- a/tests/testcollection.vala
+++ b/tests/testcollection.vala
@@ -56,6 +56,8 @@ public abstract class CollectionTests : Gee.TestCase {
 		add_test ("[Collection] all_match", test_all_match);
 		add_test ("[Collection] max_min", test_max_min);
 		add_test ("[Collection] order_by", test_order_by);
+		add_test ("[Collection] one_match", test_one_match);
+		add_test ("[Collection] count_match", test_count_match);
 	}
 
 	protected Collection<string> test_collection;
@@ -1259,5 +1261,47 @@ public abstract class CollectionTests : Gee.TestCase {
 			previous_item = item;
 		}
 	}
+
+	public void test_one_match () {
+		assert (!test_collection.one_match ((x) => x == "one"));
+
+		assert (test_collection.add ("one"));
+		assert (test_collection.one_match ((x) => x == "one"));
+		assert (!test_collection.one_match ((x) => x == "two"));
+
+		assert (test_collection.add ("two"));
+		assert (test_collection.one_match ((x) => x == "one"));
+		assert (test_collection.one_match ((x) => x == "two"));
+
+		if (test_collection.add ("two")) {
+			assert (!test_collection.one_match ((x) => x == "two"));
+		} else {
+			assert (test_collection.one_match ((x) => x == "two"));
+		}
+		assert (test_collection.one_match ((x) => x == "one"));
+
+		assert (!test_collection.one_match ((x) => x == "three"));
+	}
+
+	public void test_count_match () {
+		assert (test_collection.count_match ((x) => x == "one") == 0);
+
+		assert (test_collection.add ("one"));
+		assert (test_collection.count_match ((x) => x == "one") == 1);
+		assert (test_collection.count_match ((x) => x == "two") == 0);
+
+		assert (test_collection.add ("two"));
+		assert (test_collection.count_match ((x) => x == "one") == 1);
+		assert (test_collection.count_match ((x) => x == "two") == 1);
+
+		if (test_collection.add ("two")) {
+			assert (test_collection.count_match ((x) => x == "two") == 2);
+		} else {
+			assert (test_collection.count_match ((x) => x == "two") == 1);
+		}
+		assert (test_collection.count_match ((x) => x == "one") == 1);
+
+		assert (test_collection.count_match ((x) => x == "three") == 0);
+	}
 }