add reverse iterator to DB

[ziglmdb] / src / db.zig

diff --git a/src/db.zig b/src/db.zig
index 4062ba9db56b95b459d14e1b01f72a40c67ed8cb..4e8126de4c1c2cc23d5fd6dbdad91a5af4e14d4c 100644 (file)
--- a/src/db.zig
+++ b/src/db.zig
@@ -27,16 +27,22 @@ pub fn Db(comptime K: type, comptime V: type) type {
             return try self.dbi.has(k);
         }
         pub const Iterator = struct {
+            pub const Result = struct { key: K, val: V };
             cursor: lmdb.Cursor,
+            dir: enum { Forward, Backward },
             k: ?K,
             v: ?V,
 
-            pub fn next(self: *Iterator) ?struct { key: K, val: V } {
+            pub fn next(self: *Iterator) ?Result {
                 if (self.k != null and self.v != null) {
-                    const result = .{ .key = self.k.?, .val = self.v.? };
+                    const result = Result{ .key = self.k.?, .val = self.v.? };
 
                     var k = self.k.?;
-                    self.v = self.cursor.get(&k, V, .Next) catch return null;
+                    if (self.dir == .Forward) {
+                        self.v = self.cursor.get(&k, V, .Next) catch return null;
+                    } else {
+                        self.v = self.cursor.get(&k, V, .Prev) catch return null;
+                    }
                     if (self.v != null) {
                         self.k = k;
                     }
@@ -51,7 +57,14 @@ pub fn Db(comptime K: type, comptime V: type) type {
 
             var k: K = undefined;
             const v = try cursor.get(&k, V, .First);
-            return .{ .cursor = cursor, .k = k, .v = v };
+            return .{ .cursor = cursor, .dir = .Forward, .k = k, .v = v };
+        }
+        pub fn reverse_iterator(self: Self) !Iterator {
+            var cursor = try self.dbi.cursor();
+
+            var k: K = undefined;
+            const v = try cursor.get(&k, V, .Last);
+            return .{ .cursor = cursor, .dir = .Backward, .k = k, .v = v };
         }
     };
 }
@@ -206,13 +219,13 @@ fn SetListViewBase(comptime K: type, comptime V: type) type {
             return self.dbi.has(self.item_idx(key));
         }
         pub const Iterator = struct {
-            pub const Result = ?struct { key: K, val: V };
+            pub const Result = struct { key: K, val: V };
 
             slv: SetListViewBase(K, V),
             idx: ?K,
             dir: enum { Forward, Backward },
 
-            pub fn next(self: *Iterator) Result {
+            pub fn next(self: *Iterator) ?Result {
                 if (self.idx != null) {
                     const k = self.idx.?;
                     const item = self.slv.item_get(k) catch return null;