From 2be592bb3ca71621422428ec8874b34a77606013 Mon Sep 17 00:00:00 2001
From: Scott Redig <git@scottredig.com>
Date: Fri, 11 Sep 2026 00:54:56 -0700
Subject: [PATCH] Add EnumMap.empty, deprecate default fields

---
 lib/std/enums.zig | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/lib/std/enums.zig b/lib/std/enums.zig
index 0f7439e00961485c4ce57f8a2a6286f6a2b9c818..440f5894e55d08f87902c8a83d661fa15ece1b3d 100644
--- a/lib/std/enums.zig
+++ b/lib/std/enums.zig
@@ -420,6 +420,8 @@ pub fn EnumSet(comptime E: type) type {
 /// If the enum is exhaustive but not dense, a mapping will be constructed from
 /// enum values to dense indices.  This type does no dynamic
 /// allocation and can be copied by value.
+///
+/// Default initialization is deprecated; use .empty instead.
 pub fn EnumMap(comptime E: type, comptime V: type) type {
     return struct {
         const Self = @This();
@@ -441,6 +443,11 @@ pub fn EnumMap(comptime E: type, comptime V: type) type {
         /// bit is zero, the value is undefined.
         values: [Indexer.count]Value = undefined,
 
+        pub const empty: Self = .{
+            .bits = .empty,
+            .values = undefined,
+        };
+
         /// Initializes the map using a sparse struct of optionals
         pub fn init(init_values: EnumFieldStruct(E, ?Value, @as(?Value, null))) Self {
             @setEvalBranchQuota(2 * @typeInfo(E).@"enum".field_names.len);
@@ -470,12 +477,10 @@ pub fn EnumMap(comptime E: type, comptime V: type) type {
         /// Initializes a full mapping with all keys set to value.
         /// Consider using EnumArray instead if the map will remain full.
         pub fn initFull(value: Value) Self {
-            var result: Self = .{
+            return .{
                 .bits = .full,
-                .values = undefined,
+                .values = @splat(value),
             };
-            @memset(&result.values, value);
-            return result;
         }
 
         /// Initializes a full mapping with supplied values.
@@ -645,7 +650,10 @@ pub fn EnumMap(comptime E: type, comptime V: type) type {
 test EnumMap {
     const Ball = enum { red, green, blue };
 
-    const some = EnumMap(Ball, u8).init(.{
+    const none: EnumMap(Ball, u8) = .empty;
+    try testing.expectEqual(0, none.count());
+
+    const some: EnumMap(Ball, u8) = .init(.{
         .green = 0xff,
         .blue = 0x80,
     });
@@ -653,6 +661,9 @@ test EnumMap {
     try testing.expectEqual(null, some.get(.red));
     try testing.expectEqual(0xff, some.get(.green));
     try testing.expectEqual(0x80, some.get(.blue));
+
+    const all: EnumMap(Ball, u8) = .initFull(0);
+    try testing.expectEqual(3, all.count());
 }
 
 /// A multiset of enum elements up to a count of usize. Backed
-- 
2.54.0