ArrayListAligned

pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
    if (alignment) |a| {
        if (a.toByteUnits() == @alignOf(T)) {
            return Aligned(T, null);
        }
    }
    return struct {
        const Self = @This();
        /// Contents of the list. This field is intended to be accessed
        /// directly.
        ///
        /// Pointers to elements in this slice are invalidated by various
        /// functions of this ArrayList in accordance with the respective
        /// documentation. In all cases, "invalidated" means that the memory
        /// has been passed to an allocator's resize or free function.
        items: Slice = &[_]T{},
        /// How many T values this list can hold without allocating
        /// additional memory.
        capacity: usize = 0,

        /// An ArrayList containing no elements.
        pub const empty: Self = .{
            .items = &.{},
            .capacity = 0,
        };

        pub const Slice = if (alignment) |a| ([]align(a.toByteUnits()) T) else []T;

        pub fn SentinelSlice(comptime s: T) type {
            return if (alignment) |a| ([:s]align(a.toByteUnits()) T) else [:s]T;
        }

        /// Initialize with capacity to hold `num` elements.
        /// The resulting capacity will equal `num` exactly.
        /// Deinitialize with `deinit` or use `toOwnedSlice`.
        pub fn initCapacity(gpa: Allocator, num: usize) Allocator.Error!Self {
            var self = Self{};
            try self.ensureTotalCapacityPrecise(gpa, num);
            return self;
        }

        /// Initialize with externally-managed memory. The buffer determines the
        /// capacity, and the length is set to zero.
        ///
        /// When initialized this way, all functions that accept an Allocator
        /// argument cause illegal behavior.
        pub fn initBuffer(buffer: Slice) Self {
            return .{
                .items = buffer[0..0],
                .capacity = buffer.len,
            };
        }

        /// Release all allocated memory.
        pub fn deinit(self: *Self, gpa: Allocator) void {
            gpa.free(self.allocatedSlice());
            self.* = undefined;
        }

        /// Convert this list into an analogous memory-managed one.
        /// The returned list has ownership of the underlying memory.
        pub fn toManaged(self: *Self, gpa: Allocator) AlignedManaged(T, alignment) {
            return .{ .items = self.items, .capacity = self.capacity, .allocator = gpa };
        }

        /// ArrayList takes ownership of the passed in slice.
        /// Deinitialize with `deinit` or use `toOwnedSlice`.
        pub fn fromOwnedSlice(slice: Slice) Self {
            return Self{
                .items = slice,
                .capacity = slice.len,
            };
        }

        /// ArrayList takes ownership of the passed in slice.
        /// Deinitialize with `deinit` or use `toOwnedSlice`.
        pub fn fromOwnedSliceSentinel(comptime sentinel: T, slice: [:sentinel]T) Self {
            return Self{
                .items = slice,
                .capacity = slice.len + 1,
            };
        }

        /// The caller owns the returned memory. Empties this ArrayList.
        /// Its capacity is cleared, making deinit() safe but unnecessary to call.
        pub fn toOwnedSlice(self: *Self, gpa: Allocator) Allocator.Error!Slice {
            const old_memory = self.allocatedSlice();
            if (gpa.remap(old_memory, self.items.len)) |new_items| {
                self.* = .empty;
                return new_items;
            }

            const new_memory = try gpa.alignedAlloc(T, alignment, self.items.len);
            @memcpy(new_memory, self.items);
            self.clearAndFree(gpa);
            return new_memory;
        }

        /// The caller owns the returned memory. ArrayList becomes empty.
        pub fn toOwnedSliceSentinel(self: *Self, gpa: Allocator, comptime sentinel: T) Allocator.Error!SentinelSlice(sentinel) {
            // This addition can never overflow because `self.items` can never occupy the whole address space
            try self.ensureTotalCapacityPrecise(gpa, self.items.len + 1);
            self.appendAssumeCapacity(sentinel);
            const result = try self.toOwnedSlice(gpa);
            return result[0 .. result.len - 1 :sentinel];
        }

        /// Creates a copy of this ArrayList.
        pub fn clone(self: Self, gpa: Allocator) Allocator.Error!Self {
            var cloned = try Self.initCapacity(gpa, self.capacity);
            cloned.appendSliceAssumeCapacity(self.items);
            return cloned;
        }

        /// Insert `item` at index `i`. Moves `list[i .. list.len]` to higher indices to make room.
        /// If `i` is equal to the length of the list this operation is equivalent to append.
        /// This operation is O(N).
        /// Invalidates element pointers if additional memory is needed.
        /// Asserts that the index is in bounds or equal to the length.
        pub fn insert(self: *Self, gpa: Allocator, i: usize, item: T) Allocator.Error!void {
            const dst = try self.addManyAt(gpa, i, 1);
            dst[0] = item;
        }

        /// Insert `item` at index `i`. Moves `list[i .. list.len]` to higher indices to make room.
        ///
        /// If `i` is equal to the length of the list this operation is equivalent to append.
        ///
        /// This operation is O(N).
        ///
        /// Asserts that the list has capacity for one additional item.
        ///
        /// Asserts that the index is in bounds or equal to the length.
        pub fn insertAssumeCapacity(self: *Self, i: usize, item: T) void {
            assert(self.items.len < self.capacity);
            self.items.len += 1;

            @memmove(self.items[i + 1 .. self.items.len], self.items[i .. self.items.len - 1]);
            self.items[i] = item;
        }

        /// Insert `item` at index `i`, moving `list[i .. list.len]` to higher indices to make room.
        ///
        /// If `i` is equal to the length of the list this operation is equivalent to append.
        ///
        /// This operation is O(N).
        ///
        /// If the list lacks unused capacity for the additional item, returns
        /// `error.OutOfMemory`.
        ///
        /// Asserts that the index is in bounds or equal to the length.
        pub fn insertBounded(self: *Self, i: usize, item: T) error{OutOfMemory}!void {
            if (self.capacity - self.items.len == 0) return error.OutOfMemory;
            return insertAssumeCapacity(self, i, item);
        }

        /// Add `count` new elements at position `index`, which have
        /// `undefined` values. Returns a slice pointing to the newly allocated
        /// elements, which becomes invalid after various `ArrayList`
        /// operations.
        /// Invalidates pre-existing pointers to elements at and after `index`.
        /// Invalidates all pre-existing element pointers if capacity must be
        /// increased to accommodate the new elements.
        /// Asserts that the index is in bounds or equal to the length.
        pub fn addManyAt(
            self: *Self,
            gpa: Allocator,
            index: usize,
            count: usize,
        ) Allocator.Error![]T {
            var managed = self.toManaged(gpa);
            defer self.* = managed.moveToUnmanaged();
            return managed.addManyAt(index, count);
        }

        /// Add `count` new elements at position `index`, which have
        /// `undefined` values. Returns a slice pointing to the newly allocated
        /// elements, which becomes invalid after various `ArrayList`
        /// operations.
        /// Invalidates pre-existing pointers to elements at and after `index`, but
        /// does not invalidate any before that.
        /// Asserts that the list has capacity for the additional items.
        /// Asserts that the index is in bounds or equal to the length.
        pub fn addManyAtAssumeCapacity(self: *Self, index: usize, count: usize) []T {
            const new_len = self.items.len + count;
            assert(self.capacity >= new_len);
            const to_move = self.items[index..];
            self.items.len = new_len;
            @memmove(self.items[index + count ..][0..to_move.len], to_move);
            const result = self.items[index..][0..count];
            @memset(result, undefined);
            return result;
        }

        /// Add `count` new elements at position `index`, which have
        /// `undefined` values, returning a slice pointing to the newly
        /// allocated elements, which becomes invalid after various `ArrayList`
        /// operations.
        ///
        /// Invalidates pre-existing pointers to elements at and after `index`, but
        /// does not invalidate any before that.
        ///
        /// If the list lacks unused capacity for the additional items, returns
        /// `error.OutOfMemory`.
        ///
        /// Asserts that the index is in bounds or equal to the length.
        pub fn addManyAtBounded(self: *Self, index: usize, count: usize) error{OutOfMemory}![]T {
            if (self.capacity - self.items.len < count) return error.OutOfMemory;
            return addManyAtAssumeCapacity(self, index, count);
        }

        /// Insert slice `items` at index `i` by moving `list[i .. list.len]` to make room.
        /// This operation is O(N).
        /// Invalidates pre-existing pointers to elements at and after `index`.
        /// Invalidates all pre-existing element pointers if capacity must be
        /// increased to accommodate the new elements.
        /// Asserts that the index is in bounds or equal to the length.
        pub fn insertSlice(
            self: *Self,
            gpa: Allocator,
            index: usize,
            items: []const T,
        ) Allocator.Error!void {
            const dst = try self.addManyAt(
                gpa,
                index,
                items.len,
            );
            @memcpy(dst, items);
        }

        /// Grows or shrinks the list as necessary.
        /// Invalidates element pointers if additional capacity is allocated.
        /// Asserts that the range is in bounds.
        pub fn replaceRange(
            self: *Self,
            gpa: Allocator,
            start: usize,
            len: usize,
            new_items: []const T,
        ) Allocator.Error!void {
            const after_range = start + len;
            const range = self.items[start..after_range];
            if (range.len < new_items.len) {
                const first = new_items[0..range.len];
                const rest = new_items[range.len..];
                @memcpy(range[0..first.len], first);
                try self.insertSlice(gpa, after_range, rest);
            } else {
                self.replaceRangeAssumeCapacity(start, len, new_items);
            }
        }

        /// Grows or shrinks the list as necessary.
        ///
        /// Never invalidates element pointers.
        ///
        /// Asserts the capacity is enough for additional items.
        pub fn replaceRangeAssumeCapacity(self: *Self, start: usize, len: usize, new_items: []const T) void {
            const after_range = start + len;
            const range = self.items[start..after_range];

            if (range.len == new_items.len)
                @memcpy(range[0..new_items.len], new_items)
            else if (range.len < new_items.len) {
                const first = new_items[0..range.len];
                const rest = new_items[range.len..];
                @memcpy(range[0..first.len], first);
                const dst = self.addManyAtAssumeCapacity(after_range, rest.len);
                @memcpy(dst, rest);
            } else {
                const extra = range.len - new_items.len;
                @memcpy(range[0..new_items.len], new_items);
                const src = self.items[after_range..];
                @memmove(self.items[after_range - extra ..][0..src.len], src);
                @memset(self.items[self.items.len - extra ..], undefined);
                self.items.len -= extra;
            }
        }

        /// Grows or shrinks the list as necessary.
        ///
        /// Never invalidates element pointers.
        ///
        /// If the unused capacity is insufficient for additional items,
        /// returns `error.OutOfMemory`.
        pub fn replaceRangeBounded(self: *Self, start: usize, len: usize, new_items: []const T) error{OutOfMemory}!void {
            if (self.capacity - self.items.len < new_items.len -| len) return error.OutOfMemory;
            return replaceRangeAssumeCapacity(self, start, len, new_items);
        }

        /// Extend the list by 1 element. Allocates more memory as necessary.
        /// Invalidates element pointers if additional memory is needed.
        pub fn append(self: *Self, gpa: Allocator, item: T) Allocator.Error!void {
            const new_item_ptr = try self.addOne(gpa);
            new_item_ptr.* = item;
        }

        /// Extend the list by 1 element.
        ///
        /// Never invalidates element pointers.
        ///
        /// Asserts that the list can hold one additional item.
        pub fn appendAssumeCapacity(self: *Self, item: T) void {
            self.addOneAssumeCapacity().* = item;
        }

        /// Extend the list by 1 element.
        ///
        /// Never invalidates element pointers.
        ///
        /// If the list lacks unused capacity for the additional item, returns
        /// `error.OutOfMemory`.
        pub fn appendBounded(self: *Self, item: T) error{OutOfMemory}!void {
            if (self.capacity - self.items.len == 0) return error.OutOfMemory;
            return appendAssumeCapacity(self, item);
        }

        /// Remove the element at index `i` from the list and return its value.
        /// Invalidates pointers to the last element.
        /// This operation is O(N).
        /// Asserts that the index is in bounds.
        pub fn orderedRemove(self: *Self, i: usize) T {
            const old_item = self.items[i];
            self.replaceRangeAssumeCapacity(i, 1, &.{});
            return old_item;
        }

        /// Remove the elements indexed by `sorted_indexes`. The indexes to be
        /// removed correspond to the array list before deletion.
        ///
        /// Asserts:
        /// * Each index to be removed is in bounds.
        /// * The indexes to be removed are sorted ascending.
        ///
        /// Duplicates in `sorted_indexes` are allowed.
        ///
        /// This operation is O(N).
        ///
        /// Invalidates element pointers beyond the first deleted index.
        pub fn orderedRemoveMany(self: *Self, sorted_indexes: []const usize) void {
            if (sorted_indexes.len == 0) return;
            var shift: usize = 1;
            for (sorted_indexes[0 .. sorted_indexes.len - 1], sorted_indexes[1..]) |removed, end| {
                if (removed == end) continue; // allows duplicates in `sorted_indexes`
                const start = removed + 1;
                const len = end - start; // safety checks `sorted_indexes` are sorted
                @memmove(self.items[start - shift ..][0..len], self.items[start..][0..len]); // safety checks initial `sorted_indexes` are in range
                shift += 1;
            }
            const start = sorted_indexes[sorted_indexes.len - 1] + 1;
            const end = self.items.len;
            const len = end - start; // safety checks final `sorted_indexes` are in range
            @memmove(self.items[start - shift ..][0..len], self.items[start..][0..len]);
            self.items.len = end - shift;
        }

        /// Removes the element at the specified index and returns it.
        /// The empty slot is filled from the end of the list.
        /// Invalidates pointers to last element.
        /// This operation is O(1).
        /// Asserts that the list is not empty.
        /// Asserts that the index is in bounds.
        pub fn swapRemove(self: *Self, i: usize) T {
            if (self.items.len - 1 == i) return self.pop().?;

            const old_item = self.items[i];
            self.items[i] = self.pop().?;
            return old_item;
        }

        /// Append the slice of items to the list. Allocates more
        /// memory as necessary.
        /// Invalidates element pointers if additional memory is needed.
        pub fn appendSlice(self: *Self, gpa: Allocator, items: []const T) Allocator.Error!void {
            try self.ensureUnusedCapacity(gpa, items.len);
            self.appendSliceAssumeCapacity(items);
        }

        /// Append the slice of items to the list.
        ///
        /// Asserts that the list can hold the additional items.
        pub fn appendSliceAssumeCapacity(self: *Self, items: []const T) void {
            const old_len = self.items.len;
            const new_len = old_len + items.len;
            assert(new_len <= self.capacity);
            self.items.len = new_len;
            @memcpy(self.items[old_len..][0..items.len], items);
        }

        /// Append the slice of items to the list.
        ///
        /// If the list lacks unused capacity for the additional items, returns `error.OutOfMemory`.
        pub fn appendSliceBounded(self: *Self, items: []const T) error{OutOfMemory}!void {
            if (self.capacity - self.items.len < items.len) return error.OutOfMemory;
            return appendSliceAssumeCapacity(self, items);
        }

        /// Append the slice of items to the list. Allocates more
        /// memory as necessary. Only call this function if a call to `appendSlice` instead would
        /// be a compile error.
        /// Invalidates element pointers if additional memory is needed.
        pub fn appendUnalignedSlice(self: *Self, gpa: Allocator, items: []align(1) const T) Allocator.Error!void {
            try self.ensureUnusedCapacity(gpa, items.len);
            self.appendUnalignedSliceAssumeCapacity(items);
        }

        /// Append an unaligned slice of items to the list.
        ///
        /// Intended to be used only when `appendSliceAssumeCapacity` would be
        /// a compile error.
        ///
        /// Asserts that the list can hold the additional items.
        pub fn appendUnalignedSliceAssumeCapacity(self: *Self, items: []align(1) const T) void {
            const old_len = self.items.len;
            const new_len = old_len + items.len;
            assert(new_len <= self.capacity);
            self.items.len = new_len;
            @memcpy(self.items[old_len..][0..items.len], items);
        }

        /// Append an unaligned slice of items to the list.
        ///
        /// Intended to be used only when `appendSliceAssumeCapacity` would be
        /// a compile error.
        ///
        /// If the list lacks unused capacity for the additional items, returns
        /// `error.OutOfMemory`.
        pub fn appendUnalignedSliceBounded(self: *Self, items: []align(1) const T) error{OutOfMemory}!void {
            if (self.capacity - self.items.len < items.len) return error.OutOfMemory;
            return appendUnalignedSliceAssumeCapacity(self, items);
        }

        pub fn print(self: *Self, gpa: Allocator, comptime fmt: []const u8, args: anytype) error{OutOfMemory}!void {
            comptime assert(T == u8);
            try self.ensureUnusedCapacity(gpa, fmt.len);
            var aw: std.Io.Writer.Allocating = .fromArrayList(gpa, self);
            defer self.* = aw.toArrayList();
            return aw.writer.print(fmt, args) catch |err| switch (err) {
                error.WriteFailed => return error.OutOfMemory,
            };
        }

        pub fn printAssumeCapacity(self: *Self, comptime fmt: []const u8, args: anytype) void {
            comptime assert(T == u8);
            var w: std.io.Writer = .fixed(self.unusedCapacitySlice());
            w.print(fmt, args) catch unreachable;
            self.items.len += w.end;
        }

        pub fn printBounded(self: *Self, comptime fmt: []const u8, args: anytype) error{OutOfMemory}!void {
            comptime assert(T == u8);
            var w: std.io.Writer = .fixed(self.unusedCapacitySlice());
            w.print(fmt, args) catch return error.OutOfMemory;
            self.items.len += w.end;
        }

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        pub const WriterContext = struct {
            self: *Self,
            allocator: Allocator,
        };

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        pub const Writer = if (T != u8)
            @compileError("The Writer interface is only defined for ArrayList(u8) " ++
                "but the given type is ArrayList(" ++ @typeName(T) ++ ")")
        else
            std.io.GenericWriter(WriterContext, Allocator.Error, appendWrite);

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        pub fn writer(self: *Self, gpa: Allocator) Writer {
            return .{ .context = .{ .self = self, .allocator = gpa } };
        }

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        fn appendWrite(context: WriterContext, m: []const u8) Allocator.Error!usize {
            try context.self.appendSlice(context.allocator, m);
            return m.len;
        }

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        pub const FixedWriter = std.io.GenericWriter(*Self, Allocator.Error, appendWriteFixed);

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        pub fn fixedWriter(self: *Self) FixedWriter {
            return .{ .context = self };
        }

        /// Deprecated in favor of `print` or `std.io.Writer.Allocating`.
        fn appendWriteFixed(self: *Self, m: []const u8) error{OutOfMemory}!usize {
            const available_capacity = self.capacity - self.items.len;
            if (m.len > available_capacity)
                return error.OutOfMemory;

            self.appendSliceAssumeCapacity(m);
            return m.len;
        }

        /// Append a value to the list `n` times.
        /// Allocates more memory as necessary.
        /// Invalidates element pointers if additional memory is needed.
        /// The function is inline so that a comptime-known `value` parameter will
        /// have a more optimal memset codegen in case it has a repeated byte pattern.
        pub inline fn appendNTimes(self: *Self, gpa: Allocator, value: T, n: usize) Allocator.Error!void {
            const old_len = self.items.len;
            try self.resize(gpa, try addOrOom(old_len, n));
            @memset(self.items[old_len..self.items.len], value);
        }

        /// Append a value to the list `n` times.
        ///
        /// Never invalidates element pointers.
        ///
        /// The function is inline so that a comptime-known `value` parameter will
        /// have better memset codegen in case it has a repeated byte pattern.
        ///
        /// Asserts that the list can hold the additional items.
        pub inline fn appendNTimesAssumeCapacity(self: *Self, value: T, n: usize) void {
            const new_len = self.items.len + n;
            assert(new_len <= self.capacity);
            @memset(self.items.ptr[self.items.len..new_len], value);
            self.items.len = new_len;
        }

        /// Append a value to the list `n` times.
        ///
        /// Never invalidates element pointers.
        ///
        /// The function is inline so that a comptime-known `value` parameter will
        /// have better memset codegen in case it has a repeated byte pattern.
        ///
        /// If the list lacks unused capacity for the additional items, returns
        /// `error.OutOfMemory`.
        pub inline fn appendNTimesBounded(self: *Self, value: T, n: usize) error{OutOfMemory}!void {
            const new_len = self.items.len + n;
            if (self.capacity < new_len) return error.OutOfMemory;
            @memset(self.items.ptr[self.items.len..new_len], value);
            self.items.len = new_len;
        }

        /// Adjust the list length to `new_len`.
        /// Additional elements contain the value `undefined`.
        /// Invalidates element pointers if additional memory is needed.
        pub fn resize(self: *Self, gpa: Allocator, new_len: usize) Allocator.Error!void {
            try self.ensureTotalCapacity(gpa, new_len);
            self.items.len = new_len;
        }

        /// Reduce allocated capacity to `new_len`.
        /// May invalidate element pointers.
        /// Asserts that the new length is less than or equal to the previous length.
        pub fn shrinkAndFree(self: *Self, gpa: Allocator, new_len: usize) void {
            assert(new_len <= self.items.len);

            if (@sizeOf(T) == 0) {
                self.items.len = new_len;
                return;
            }

            const old_memory = self.allocatedSlice();
            if (gpa.remap(old_memory, new_len)) |new_items| {
                self.capacity = new_items.len;
                self.items = new_items;
                return;
            }

            const new_memory = gpa.alignedAlloc(T, alignment, new_len) catch |e| switch (e) {
                error.OutOfMemory => {
                    // No problem, capacity is still correct then.
                    self.items.len = new_len;
                    return;
                },
            };

            @memcpy(new_memory, self.items[0..new_len]);
            gpa.free(old_memory);
            self.items = new_memory;
            self.capacity = new_memory.len;
        }

        /// Reduce length to `new_len`.
        /// Invalidates pointers to elements `items[new_len..]`.
        /// Keeps capacity the same.
        /// Asserts that the new length is less than or equal to the previous length.
        pub fn shrinkRetainingCapacity(self: *Self, new_len: usize) void {
            assert(new_len <= self.items.len);
            self.items.len = new_len;
        }

        /// Invalidates all element pointers.
        pub fn clearRetainingCapacity(self: *Self) void {
            self.items.len = 0;
        }

        /// Invalidates all element pointers.
        pub fn clearAndFree(self: *Self, gpa: Allocator) void {
            gpa.free(self.allocatedSlice());
            self.items.len = 0;
            self.capacity = 0;
        }

        /// Modify the array so that it can hold at least `new_capacity` items.
        /// Implements super-linear growth to achieve amortized O(1) append operations.
        /// Invalidates element pointers if additional memory is needed.
        pub fn ensureTotalCapacity(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
            if (self.capacity >= new_capacity) return;
            return self.ensureTotalCapacityPrecise(gpa, growCapacity(self.capacity, new_capacity));
        }

        /// If the current capacity is less than `new_capacity`, this function will
        /// modify the array so that it can hold exactly `new_capacity` items.
        /// Invalidates element pointers if additional memory is needed.
        pub fn ensureTotalCapacityPrecise(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
            if (@sizeOf(T) == 0) {
                self.capacity = math.maxInt(usize);
                return;
            }

            if (self.capacity >= new_capacity) return;

            // Here we avoid copying allocated but unused bytes by
            // attempting a resize in place, and falling back to allocating
            // a new buffer and doing our own copy. With a realloc() call,
            // the allocator implementation would pointlessly copy our
            // extra capacity.
            const old_memory = self.allocatedSlice();
            if (gpa.remap(old_memory, new_capacity)) |new_memory| {
                self.items.ptr = new_memory.ptr;
                self.capacity = new_memory.len;
            } else {
                const new_memory = try gpa.alignedAlloc(T, alignment, new_capacity);
                @memcpy(new_memory[0..self.items.len], self.items);
                gpa.free(old_memory);
                self.items.ptr = new_memory.ptr;
                self.capacity = new_memory.len;
            }
        }

        /// Modify the array so that it can hold at least `additional_count` **more** items.
        /// Invalidates element pointers if additional memory is needed.
        pub fn ensureUnusedCapacity(
            self: *Self,
            gpa: Allocator,
            additional_count: usize,
        ) Allocator.Error!void {
            return self.ensureTotalCapacity(gpa, try addOrOom(self.items.len, additional_count));
        }

        /// Increases the array's length to match the full capacity that is already allocated.
        /// The new elements have `undefined` values.
        /// Never invalidates element pointers.
        pub fn expandToCapacity(self: *Self) void {
            self.items.len = self.capacity;
        }

        /// Increase length by 1, returning pointer to the new item.
        /// The returned element pointer becomes invalid when the list is resized.
        pub fn addOne(self: *Self, gpa: Allocator) Allocator.Error!*T {
            // This can never overflow because `self.items` can never occupy the whole address space
            const newlen = self.items.len + 1;
            try self.ensureTotalCapacity(gpa, newlen);
            return self.addOneAssumeCapacity();
        }

        /// Increase length by 1, returning pointer to the new item.
        ///
        /// Never invalidates element pointers.
        ///
        /// The returned element pointer becomes invalid when the list is resized.
        ///
        /// Asserts that the list can hold one additional item.
        pub fn addOneAssumeCapacity(self: *Self) *T {
            assert(self.items.len < self.capacity);

            self.items.len += 1;
            return &self.items[self.items.len - 1];
        }

        /// Increase length by 1, returning pointer to the new item.
        ///
        /// Never invalidates element pointers.
        ///
        /// The returned element pointer becomes invalid when the list is resized.
        ///
        /// If the list lacks unused capacity for the additional item, returns `error.OutOfMemory`.
        pub fn addOneBounded(self: *Self) error{OutOfMemory}!*T {
            if (self.capacity - self.items.len < 1) return error.OutOfMemory;
            return addOneAssumeCapacity(self);
        }

        /// Resize the array, adding `n` new elements, which have `undefined` values.
        /// The return value is an array pointing to the newly allocated elements.
        /// The returned pointer becomes invalid when the list is resized.
        pub fn addManyAsArray(self: *Self, gpa: Allocator, comptime n: usize) Allocator.Error!*[n]T {
            const prev_len = self.items.len;
            try self.resize(gpa, try addOrOom(self.items.len, n));
            return self.items[prev_len..][0..n];
        }

        /// Resize the array, adding `n` new elements, which have `undefined` values.
        ///
        /// The return value is an array pointing to the newly allocated elements.
        ///
        /// Never invalidates element pointers.
        ///
        /// The returned pointer becomes invalid when the list is resized.
        ///
        /// Asserts that the list can hold the additional items.
        pub fn addManyAsArrayAssumeCapacity(self: *Self, comptime n: usize) *[n]T {
            assert(self.items.len + n <= self.capacity);
            const prev_len = self.items.len;
            self.items.len += n;
            return self.items[prev_len..][0..n];
        }

        /// Resize the array, adding `n` new elements, which have `undefined` values.
        ///
        /// The return value is an array pointing to the newly allocated elements.
        ///
        /// Never invalidates element pointers.
        ///
        /// The returned pointer becomes invalid when the list is resized.
        ///
        /// If the list lacks unused capacity for the additional items, returns
        /// `error.OutOfMemory`.
        pub fn addManyAsArrayBounded(self: *Self, comptime n: usize) error{OutOfMemory}!*[n]T {
            if (self.capacity - self.items.len < n) return error.OutOfMemory;
            return addManyAsArrayAssumeCapacity(self, n);
        }

        /// Resize the array, adding `n` new elements, which have `undefined` values.
        /// The return value is a slice pointing to the newly allocated elements.
        /// The returned pointer becomes invalid when the list is resized.
        /// Resizes list if `self.capacity` is not large enough.
        pub fn addManyAsSlice(self: *Self, gpa: Allocator, n: usize) Allocator.Error![]T {
            const prev_len = self.items.len;
            try self.resize(gpa, try addOrOom(self.items.len, n));
            return self.items[prev_len..][0..n];
        }

        /// Resizes the array, adding `n` new elements, which have `undefined`
        /// values, returning a slice pointing to the newly allocated elements.
        ///
        /// Never invalidates element pointers. The returned pointer becomes
        /// invalid when the list is resized.
        ///
        /// Asserts that the list can hold the additional items.
        pub fn addManyAsSliceAssumeCapacity(self: *Self, n: usize) []T {
            assert(self.items.len + n <= self.capacity);
            const prev_len = self.items.len;
            self.items.len += n;
            return self.items[prev_len..][0..n];
        }

        /// Resizes the array, adding `n` new elements, which have `undefined`
        /// values, returning a slice pointing to the newly allocated elements.
        ///
        /// Never invalidates element pointers. The returned pointer becomes
        /// invalid when the list is resized.
        ///
        /// If the list lacks unused capacity for the additional items, returns
        /// `error.OutOfMemory`.
        pub fn addManyAsSliceBounded(self: *Self, n: usize) error{OutOfMemory}![]T {
            if (self.capacity - self.items.len < n) return error.OutOfMemory;
            return addManyAsSliceAssumeCapacity(self, n);
        }

        /// Remove and return the last element from the list.
        /// If the list is empty, returns `null`.
        /// Invalidates pointers to last element.
        pub fn pop(self: *Self) ?T {
            if (self.items.len == 0) return null;
            const val = self.items[self.items.len - 1];
            self.items.len -= 1;
            return val;
        }

        /// Returns a slice of all the items plus the extra capacity, whose memory
        /// contents are `undefined`.
        pub fn allocatedSlice(self: Self) Slice {
            return self.items.ptr[0..self.capacity];
        }

        /// Returns a slice of only the extra capacity after items.
        /// This can be useful for writing directly into an ArrayList.
        /// Note that such an operation must be followed up with a direct
        /// modification of `self.items.len`.
        pub fn unusedCapacitySlice(self: Self) []T {
            return self.allocatedSlice()[self.items.len..];
        }

        /// Return the last element from the list.
        /// Asserts that the list is not empty.
        pub fn getLast(self: Self) T {
            const val = self.items[self.items.len - 1];
            return val;
        }

        /// Return the last element from the list, or
        /// return `null` if list is empty.
        pub fn getLastOrNull(self: Self) ?T {
            if (self.items.len == 0) return null;
            return self.getLast();
        }

        const init_capacity = @as(comptime_int, @max(1, std.atomic.cache_line / @sizeOf(T)));

        /// Called when memory growth is necessary. Returns a capacity larger than
        /// minimum that grows super-linearly.
        fn growCapacity(current: usize, minimum: usize) usize {
            var new = current;
            while (true) {
                new +|= new / 2 + init_capacity;
                if (new >= minimum)
                    return new;
            }
        }
    };
}