EnumArray

pub fn EnumArray(comptime E: type, comptime V: type) type {
    return struct {
        const Self = @This();

        /// The index mapping for this map
        pub const Indexer = EnumIndexer(E);
        /// The key type used to index this map
        pub const Key = Indexer.Key;
        /// The value type stored in this map
        pub const Value = V;
        /// The number of possible keys in the map
        pub const len = Indexer.count;

        values: [Indexer.count]Value,

        pub fn init(init_values: EnumFieldStruct(E, Value, null)) Self {
            return initDefault(null, init_values);
        }

        /// Initializes values in the enum array, with the specified default.
        pub fn initDefault(comptime default: ?Value, init_values: EnumFieldStruct(E, Value, default)) Self {
            @setEvalBranchQuota(2 * @typeInfo(E).@"enum".fields.len);
            var result: Self = .{ .values = undefined };
            inline for (0..Self.len) |i| {
                const key = comptime Indexer.keyForIndex(i);
                const tag = @tagName(key);
                result.values[i] = @field(init_values, tag);
            }
            return result;
        }

        pub fn initUndefined() Self {
            return Self{ .values = undefined };
        }

        pub fn initFill(v: Value) Self {
            var self: Self = undefined;
            @memset(&self.values, v);
            return self;
        }

        /// Returns the value in the array associated with a key.
        pub fn get(self: Self, key: Key) Value {
            return self.values[Indexer.indexOf(key)];
        }

        /// Returns a pointer to the slot in the array associated with a key.
        pub fn getPtr(self: *Self, key: Key) *Value {
            return &self.values[Indexer.indexOf(key)];
        }

        /// Returns a const pointer to the slot in the array associated with a key.
        pub fn getPtrConst(self: *const Self, key: Key) *const Value {
            return &self.values[Indexer.indexOf(key)];
        }

        /// Sets the value in the slot associated with a key.
        pub fn set(self: *Self, key: Key, value: Value) void {
            self.values[Indexer.indexOf(key)] = value;
        }

        /// Iterates over the items in the array, in index order.
        pub fn iterator(self: *Self) Iterator {
            return .{
                .values = &self.values,
            };
        }

        /// An entry in the array.
        pub const Entry = struct {
            /// The key associated with this entry.
            /// Modifying this key will not change the array.
            key: Key,

            /// A pointer to the value in the array associated
            /// with this key.  Modifications through this
            /// pointer will modify the underlying data.
            value: *Value,
        };

        pub const Iterator = struct {
            index: usize = 0,
            values: *[Indexer.count]Value,

            pub fn next(self: *Iterator) ?Entry {
                const index = self.index;
                if (index < Indexer.count) {
                    self.index += 1;
                    return Entry{
                        .key = Indexer.keyForIndex(index),
                        .value = &self.values[index],
                    };
                }
                return null;
            }
        };
    };
}