[libgee] Introduce immutable empty collection, list, set and map

[Didier Villevalois <dvillevalois src gnome org>]

commit 9968b87f3bd6f0521dc046683448e50ffa7bb87a
Author: Didier 'Ptitjes <ptitjes free fr>
Date:   Thu Sep 24 00:41:14 2009 +0200

    Introduce immutable empty collection, list, set and map

 gee/collection.vala |    9 +++++++++
 gee/list.vala       |    9 +++++++++
 gee/map.vala        |    9 +++++++++
 gee/set.vala        |    8 ++++++++
 4 files changed, 35 insertions(+), 0 deletions(-)
---
diff --git a/gee/collection.vala b/gee/collection.vala
index d70da7a..32dd0ad 100644
--- a/gee/collection.vala
+++ b/gee/collection.vala
@@ -126,5 +126,14 @@ public interface Gee.Collection<G> : Iterable<G> {
 	 * Property giving access to the read-only view of this collection.
 	 */
 	public abstract Collection<G> read_only_view { owned get; }
+
+	/**
+	 * Returns an immutable empty collection.
+	 *
+	 * @return an immutable empty collection
+	 */
+	public static Collection<G> empty<G> () {
+		return new HashSet<G> ().read_only_view;
+	}
 }
 
diff --git a/gee/list.vala b/gee/list.vala
index eae18b1..c6e74e1 100644
--- a/gee/list.vala
+++ b/gee/list.vala
@@ -117,5 +117,14 @@ public interface Gee.List<G> : Collection<G> {
 	 * Property giving access to the read-only view of this list.
 	 */
 	public abstract new List<G> read_only_view { owned get; }
+
+	/**
+	 * Returns an immutable empty list.
+	 *
+	 * @return an immutable empty list
+	 */
+	public static List<G> empty<G> () {
+		return new LinkedList<G> ().read_only_view;
+	}
 }
 
diff --git a/gee/map.vala b/gee/map.vala
index c3b244a..f085c5f 100644
--- a/gee/map.vala
+++ b/gee/map.vala
@@ -188,5 +188,14 @@ public interface Gee.Map<K,V> : GLib.Object, Iterable<Map.Entry<K,V>> {
 	 * Property giving access to the read-only view this map.
 	 */
 	public abstract Map<K,V> read_only_view { owned get; }
+
+	/**
+	 * Returns an immutable empty map.
+	 *
+	 * @return an immutable empty map
+	 */
+	public static Map<K,V> empty<K,V> () {
+		return new HashMap<K,V> ().read_only_view;
+	}
 }
 
diff --git a/gee/set.vala b/gee/set.vala
index 15e8ff6..019d906 100644
--- a/gee/set.vala
+++ b/gee/set.vala
@@ -30,5 +30,13 @@ public interface Gee.Set<G> : Collection<G> {
 	 */
 	public abstract new Set<G> read_only_view { owned get; }
 
+	/**
+	 * Returns an immutable empty set.
+	 *
+	 * @return an immutable empty set
+	 */
+	public static Set<G> empty<G> () {
+		return new HashSet<G> ().read_only_view;
+	}
 }