Added... len... Yes

src/fixed_slot_map.zig

@@ -96,11 +96,11 @@ pub fn FixedSlotMap(
         /// Skips slots that live on the free list ( `󰮢` tombstones `󰮢` )
         /// ----------------------------------------------------
         fn nextLive(
-            len: usize,
+            n: usize,
             free_list: []const u32,
             index: *usize,
         ) ?usize {
-            while (index.* < len) : (index.* += 1) {
+            while (index.* < n) : (index.* += 1) {
                 if (std.mem.indexOfScalar(u32, free_list, @intCast(index.*)) == null) {
                     const i = index.*;
                     index.* += 1;
@@ -207,6 +207,14 @@ pub fn FixedSlotMap(
             return self.get(handle) != null;
         }
 
+        /// ----------------------------------------------------
+        /// Number of live entries
+        /// Removed (freed) slots are not counted
+        /// ----------------------------------------------------
+        pub fn len(self: *Self) usize {
+            return self.values.items().len - self.free_list.items().len;
+        }
+
         /// ----------------------------------------------------
         /// ----------------------------------------------------
         pub fn iterator(self: *Self) Iterator {

src/keyed_slot_map.zig

@@ -116,11 +116,11 @@ pub fn KeyedSlotMap(
         /// Skips slots that live on the free list ( `󰮢` tombstones `󰮢` rip-bozo 😭 )
         /// ----------------------------------------------------
         fn nextLive(
-            len: usize,
+            n: usize,
             free_list: []const u32,
             index: *usize,
         ) ?usize {
-            while (index.* < len) : (index.* += 1) {
+            while (index.* < n) : (index.* += 1) {
                 if (std.mem.indexOfScalar(u32, free_list, @intCast(index.*)) == null) {
                     const i = index.*;
                     index.* += 1;
@@ -267,6 +267,14 @@ pub fn KeyedSlotMap(
             return @intCast(self.lookup.count());
         }
 
+        /// ----------------------------------------------------
+        /// Number of live entries
+        /// Removed (freed) slots are not counted
+        /// ----------------------------------------------------
+        pub fn len(self: *const Self) usize {
+            return self.slot_map.values.items.len - self.slot_map.free_list.items.len;
+        }
+
         /// ----------------------------------------------------
         /// ----------------------------------------------------
         pub fn iterator(self: *Self) Iterator {

src/slot_map.zig

@@ -90,11 +90,11 @@ pub fn SlotMap(comptime T: type) type {
         /// Skips slots that live on the free list ( `󰮢` tombstones `󰮢` )
         /// ----------------------------------------------------
         fn nextLive(
-            len: usize,
+            n: usize,
             free_list: []const u32,
             index: *usize,
         ) ?usize {
-            while (index.* < len) : (index.* += 1) {
+            while (index.* < n) : (index.* += 1) {
                 if (std.mem.indexOfScalar(u32, free_list, @intCast(index.*)) == null) {
                     const i = index.*;
                     index.* += 1;
@@ -207,6 +207,14 @@ pub fn SlotMap(comptime T: type) type {
             return self.get(handle) != null;
         }
 
+        /// ----------------------------------------------------
+        /// Number of live entries
+        /// Removed (freed) slots are not counted
+        /// ----------------------------------------------------
+        pub fn len(self: *const Self) usize {
+            return self.values.items.len - self.free_list.items.len;
+        }
+
         /// ----------------------------------------------------
         /// ----------------------------------------------------
         pub fn iterator(self: *Self) Iterator {