    const std = @import("std.zig");
    const StringHashMap = std.StringHashMap;
    const mem = std.mem;
    const Allocator = mem.Allocator;
    const testing = std.testing;

    /// BufMap copies keys and values before they go into the map, and
    /// frees them when they get removed.
    pub const BufMap = struct {
        hash_map: BufMapHashMap,

        const BufMapHashMap = StringHashMap([]const u8);

        /// Create a BufMap backed by a specific allocator.
        /// That allocator will be used for both backing allocations
        /// and string deduplication.
        pub fn init(allocator: Allocator) BufMap {
            var self = BufMap{ .hash_map = BufMapHashMap.init(allocator) };
            return self;
        }

        /// Free the backing storage of the map, as well as all
        /// of the stored keys and values.
        pub fn deinit(self: *BufMap) void {
            var it = self.hash_map.iterator();
            while (it.next()) |entry| {
                self.free(entry.key_ptr.*);
                self.free(entry.value_ptr.*);
            }

            self.hash_map.deinit();
        }

        /// Same as `put` but the key and value become owned by the BufMap rather
        /// than being copied.
        /// If `putMove` fails, the ownership of key and value does not transfer.
        pub fn putMove(self: *BufMap, key: []u8, value: []u8) !void {
            const get_or_put = try self.hash_map.getOrPut(key);
            if (get_or_put.found_existing) {
                self.free(get_or_put.key_ptr.*);
                self.free(get_or_put.value_ptr.*);
                get_or_put.key_ptr.* = key;
            }
            get_or_put.value_ptr.* = value;
        }

        /// `key` and `value` are copied into the BufMap.
        pub fn put(self: *BufMap, key: []const u8, value: []const u8) !void {
            const value_copy = try self.copy(value);
            errdefer self.free(value_copy);
            const get_or_put = try self.hash_map.getOrPut(key);
            if (get_or_put.found_existing) {
                self.free(get_or_put.value_ptr.*);
            } else {
                get_or_put.key_ptr.* = self.copy(key) catch |err| {
                    _ = self.hash_map.remove(key);
                    return err;
                };
            }
            get_or_put.value_ptr.* = value_copy;
        }

        /// Find the address of the value associated with a key.
        /// The returned pointer is invalidated if the map resizes.
        pub fn getPtr(self: BufMap, key: []const u8) ?*[]const u8 {
            return self.hash_map.getPtr(key);
        }

        /// Return the map's copy of the value associated with
        /// a key.  The returned string is invalidated if this
        /// key is removed from the map.
        pub fn get(self: BufMap, key: []const u8) ?[]const u8 {
            return self.hash_map.get(key);
        }

        /// Removes the item from the map and frees its value.
        /// This invalidates the value returned by get() for this key.
        pub fn remove(self: *BufMap, key: []const u8) void {
            const kv = self.hash_map.fetchRemove(key) orelse return;
            self.free(kv.key);
            self.free(kv.value);
        }

        /// Returns the number of KV pairs stored in the map.
        pub fn count(self: BufMap) BufMapHashMap.Size {
            return self.hash_map.count();
        }

        /// Returns an iterator over entries in the map.
        pub fn iterator(self: *const BufMap) BufMapHashMap.Iterator {
            return self.hash_map.iterator();
        }

        fn free(self: BufMap, value: []const u8) void {
            self.hash_map.allocator.free(value);
        }

        fn copy(self: BufMap, value: []const u8) ![]u8 {
            return self.hash_map.allocator.dupe(u8, value);
        }
    };

    test "BufMap" {
        const allocator = std.testing.allocator;
        var bufmap = BufMap.init(allocator);
        defer bufmap.deinit();

        try bufmap.put("x", "1");
        try testing.expect(mem.eql(u8, bufmap.get("x").?, "1"));
        try testing.expect(1 == bufmap.count());

        try bufmap.put("x", "2");
        try testing.expect(mem.eql(u8, bufmap.get("x").?, "2"));
        try testing.expect(1 == bufmap.count());

        try bufmap.put("x", "3");
        try testing.expect(mem.eql(u8, bufmap.get("x").?, "3"));
        try testing.expect(1 == bufmap.count());

        bufmap.remove("x");
        try testing.expect(0 == bufmap.count());

        try bufmap.putMove(try allocator.dupe(u8, "k"), try allocator.dupe(u8, "v1"));
        try bufmap.putMove(try allocator.dupe(u8, "k"), try allocator.dupe(u8, "v2"));
    }