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

    /// A BufSet is a set of strings.  The BufSet duplicates
    /// strings internally, and never takes ownership of strings
    /// which are passed to it.
    pub const BufSet = struct {
        hash_map: BufSetHashMap,

        const BufSetHashMap = StringHashMap(void);
        pub const Iterator = BufSetHashMap.KeyIterator;

        /// Create a BufSet using an allocator.  The allocator will
        /// be used internally for both backing allocations and
        /// string duplication.
        pub fn init(a: Allocator) BufSet {
            var self = BufSet{ .hash_map = BufSetHashMap.init(a) };
            return self;
        }

        /// Free a BufSet along with all stored keys.
        pub fn deinit(self: *BufSet) void {
            var it = self.hash_map.keyIterator();
            while (it.next()) |key_ptr| {
                self.free(key_ptr.*);
            }
            self.hash_map.deinit();
            self.* = undefined;
        }

        /// Insert an item into the BufSet.  The item will be
        /// copied, so the caller may delete or reuse the
        /// passed string immediately.
        pub fn insert(self: *BufSet, value: []const u8) !void {
            const gop = try self.hash_map.getOrPut(value);
            if (!gop.found_existing) {
                gop.key_ptr.* = self.copy(value) catch |err| {
                    _ = self.hash_map.remove(value);
                    return err;
                };
            }
        }

        /// Check if the set contains an item matching the passed string
        pub fn contains(self: BufSet, value: []const u8) bool {
            return self.hash_map.contains(value);
        }

        /// Remove an item from the set.
        pub fn remove(self: *BufSet, value: []const u8) void {
            const kv = self.hash_map.fetchRemove(value) orelse return;
            self.free(kv.key);
        }

        /// Returns the number of items stored in the set
        pub fn count(self: *const BufSet) usize {
            return self.hash_map.count();
        }

        /// Returns an iterator over the items stored in the set.
        /// Iteration order is arbitrary.
        pub fn iterator(self: *const BufSet) Iterator {
            return self.hash_map.keyIterator();
        }

        /// Get the allocator used by this set
        pub fn allocator(self: *const BufSet) Allocator {
            return self.hash_map.allocator;
        }

        /// Creates a copy of this BufSet, using a specified allocator.
        pub fn cloneWithAllocator(
            self: *const BufSet,
            new_allocator: Allocator,
        ) Allocator.Error!BufSet {
            var cloned_hashmap = try self.hash_map.cloneWithAllocator(new_allocator);
            var cloned = BufSet{ .hash_map = cloned_hashmap };
            var it = cloned.hash_map.keyIterator();
            while (it.next()) |key_ptr| {
                key_ptr.* = try cloned.copy(key_ptr.*);
            }

            return cloned;
        }

        /// Creates a copy of this BufSet, using the same allocator.
        pub fn clone(self: *const BufSet) Allocator.Error!BufSet {
            return self.cloneWithAllocator(self.allocator());
        }

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

        fn copy(self: *const BufSet, value: []const u8) ![]const u8 {
            const result = try self.hash_map.allocator.alloc(u8, value.len);
            @memcpy(result, value);
            return result;
        }
    };

    test "BufSet" {
        var bufset = BufSet.init(std.testing.allocator);
        defer bufset.deinit();

        try bufset.insert("x");
        try testing.expect(bufset.count() == 1);
        bufset.remove("x");
        try testing.expect(bufset.count() == 0);

        try bufset.insert("x");
        try bufset.insert("y");
        try bufset.insert("z");
    }

    test "BufSet clone" {
        var original = BufSet.init(testing.allocator);
        defer original.deinit();
        try original.insert("x");

        var cloned = try original.clone();
        defer cloned.deinit();
        cloned.remove("x");
        try testing.expect(original.count() == 1);
        try testing.expect(cloned.count() == 0);

        try testing.expectError(
            error.OutOfMemory,
            original.cloneWithAllocator(testing.failing_allocator),
        );
    }

    test "BufSet.clone with arena" {
        var allocator = std.testing.allocator;
        var arena = std.heap.ArenaAllocator.init(allocator);
        defer arena.deinit();

        var buf = BufSet.init(allocator);
        defer buf.deinit();
        try buf.insert("member1");
        try buf.insert("member2");

        _ = try buf.cloneWithAllocator(arena.allocator());
    }