Commit 86a9a9048e28efc8b49d42db12db123822c3450b | zig

author	Rue04 <iokg04@gmail.com> 2026-01-03 20:32:07+01:00
committer	Rue04 <iokg04@gmail.com> 2026-01-04 03:05:34+01:00
log	86a9a9048e28efc8b49d42db12db123822c3450b
tree	5b1190726ce64d5f019d0dd732deaa334d398062
parent	0cbaaa5eb9434eb9484bae95949a4086eb472c6a

`std.MultiArrayList`: add `*Bounded` variants and `initCapacity`

Because I accidentially squished two commit and can't figure out how to separate them
again, this also
- standardizes some doc-comments
- makes a slight change to `std.ArrayList`'s `initCapacity`'s doc-comment

2 files changed, 94 insertions(+), 38 deletions(-)

lib
- std
  - array_list.zig
  - multi_array_list.zig

lib/std/array_list.zig+3-4

 @@ -599,11 +599,10 @@ pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
             return if (alignment) |a| ([:s]align(a.toByteUnits()) T) else [:s]T;
         }
-        /// Initialize with capacity to hold `num` elements.
+        /// Initialize with capacity to hold exactly `num` elements.
-        /// The resulting capacity will equal `num` exactly.
+        /// Deinitialize with `deinit` or `toOwnedSlice`.
-        /// Deinitialize with `deinit` or use `toOwnedSlice`.
         pub fn initCapacity(gpa: Allocator, num: usize) Allocator.Error!Self {
-            var self = Self{};
+            var self: Self = .empty;
             try self.ensureTotalCapacityPrecise(gpa, num);
             return self;
         }

lib/std/multi_array_list.zig+91-34

 @@ -29,6 +29,14 @@ pub fn MultiArrayList(comptime T: type) type {
             .capacity = 0,
         };
+        /// Initialize with capacity to hold exactly `num` elements.
+        /// Deinitialize with `deinit` or `toOwnedSlice`.
+        pub fn initCapacity(gpa: Allocator, num: usize) Allocator.Error!Self {
+            var self: Self = .empty;
+            try self.setCapacity(gpa, num);
+            return self;
+        }
         const Elem = switch (@typeInfo(T)) {
             .@"struct" => T,
             .@"union" => |u| struct {
 @@ -253,31 +261,45 @@ pub fn MultiArrayList(comptime T: type) type {
             return self.slice().get(index);
         }
-        /// Extend the list by 1 element. Allocates more memory as necessary.
+        /// Extend the list by 1 element.
-        pub fn append(self: *Self, gpa: Allocator, elem: T) !void {
+        ///
+        /// Allocates more memory as necessary.
+        pub fn append(self: *Self, gpa: Allocator, elem: T) Allocator.Error!void {
             try self.ensureUnusedCapacity(gpa, 1);
             self.appendAssumeCapacity(elem);
         }
-        /// Extend the list by 1 element, but asserting `self.capacity`
+        /// Extend the list by 1 element.
-        /// is sufficient to hold an additional item.
+        ///
+        /// Asserts that capacity is sufficient to hold an additional item.
         pub fn appendAssumeCapacity(self: *Self, elem: T) void {
             assert(self.len < self.capacity);
             self.len += 1;
             self.set(self.len - 1, elem);
         }
+        /// Extend the list by 1 element.
+        ///
+        /// If capacity is not sufficient to hold an additional
+        /// item, returns `error.OutOfMemory`.
+        pub fn appendBounded(self: *Self, elem: T) error{OutOfMemory}!void {
+            if (self.capacity - self.len < 1) return error.OutOfMemory;
+            return appendAssumeCapacity(self, elem);
+        }
         /// Extend the list by 1 element, returning the newly reserved
         /// index with uninitialized data.
-        /// Allocates more memory as necesasry.
+        ///
+        /// Allocates more memory as necessary.
         pub fn addOne(self: *Self, gpa: Allocator) Allocator.Error!usize {
             try self.ensureUnusedCapacity(gpa, 1);
             return self.addOneAssumeCapacity();
         }
-        /// Extend the list by 1 element, asserting `self.capacity`
+        /// Extend the list by 1 element, returning the newly reserved
-        /// is sufficient to hold an additional item.  Returns the
+        /// index with uninitialized data.
-        /// newly reserved index with uninitialized data.
+        ///
+        /// Asserts that capacity is sufficient to hold an additional item.
         pub fn addOneAssumeCapacity(self: *Self) usize {
             assert(self.len < self.capacity);
             const index = self.len;
 @@ -285,6 +307,16 @@ pub fn MultiArrayList(comptime T: type) type {
             return index;
         }
+        /// Extend the list by 1 element, returning the newly reserved
+        /// index with uninitialized data.
+        ///
+        /// If capacity is not sufficient to hold an additional
+        /// item, returns `error.OutOfMemory`.
+        pub fn addOneBounded(self: *Self) error{OutOfMemory}!usize {
+            if (self.capacity - self.len < 1) return error.OutOfMemory;
+            return addOneAssumeCapacity(self);
+        }
         /// Remove and return the last element from the list, or return `null` if list is empty.
         /// Invalidates pointers to fields of the removed element.
         pub fn pop(self: *Self) ?T {
 @@ -294,19 +326,21 @@ pub fn MultiArrayList(comptime T: type) type {
             return val;
         }
-        /// Inserts an item into an ordered list.  Shifts all elements
+        /// Inserts an item into the list. Shifts all elements
         /// after and including the specified index back by one and
-        /// sets the given index to the specified element.  May reallocate
+        /// sets the given index to the specified element.
-        /// and invalidate iterators.
+        ///
+        /// Allocates more memory as necessary.
         pub fn insert(self: *Self, gpa: Allocator, index: usize, elem: T) !void {
             try self.ensureUnusedCapacity(gpa, 1);
             self.insertAssumeCapacity(index, elem);
         }
-        /// Inserts an item into an ordered list which has room for it.
+        /// Inserts an item into the list. Shifts all elements
-        /// Shifts all elements after and including the specified index
+        /// after and including the specified index back by one and
-        /// back by one and sets the given index to the specified element.
+        /// sets the given index to the specified element.
-        /// Will not reallocate the array, does not invalidate iterators.
+        ///
+        /// Asserts that capacity is sufficient to hold an additional item.
         pub fn insertAssumeCapacity(self: *Self, index: usize, elem: T) void {
             assert(self.len < self.capacity);
             assert(index <= self.len);
 @@ -327,8 +361,19 @@ pub fn MultiArrayList(comptime T: type) type {
             }
         }
+        /// Inserts an item into the list. Shifts all elements
+        /// after and including the specified index back by one and
+        /// sets the given index to the specified element.
+        ///
+        /// If capacity is not sufficient to hold an additional
+        /// item, returns `error.OutOfMemory`.
+        pub fn insertBounded(self: *Self, index: usize, elem: T) error{OutOfMemory}!void {
+            if (self.capacity - self.len < 1) return error.OutOfMemory;
+            return insertAssumeCapacity(self, index, elem);
+        }
         /// Remove the specified item from the list, swapping the last
-        /// item in the list into its position.  Fast, but does not
+        /// item in the list into its position. Fast, but does not
         /// retain list ordering.
         pub fn swapRemove(self: *Self, index: usize) void {
             const slices = self.slice();
 @@ -393,7 +438,7 @@ pub fn MultiArrayList(comptime T: type) type {
         /// Adjust the list's length to `new_len`.
         /// Does not initialize added items, if any.
-        pub fn resize(self: *Self, gpa: Allocator, new_len: usize) !void {
+        pub fn resize(self: *Self, gpa: Allocator, new_len: usize) Allocator.Error!void {
             try self.ensureTotalCapacity(gpa, new_len);
             self.len = new_len;
         }
 @@ -479,14 +524,14 @@ pub fn MultiArrayList(comptime T: type) type {
         /// Modify the array so that it can hold at least `additional_count` **more** items.
         /// Invalidates pointers if additional memory is needed.
-        pub fn ensureUnusedCapacity(self: *Self, gpa: Allocator, additional_count: usize) !void {
+        pub fn ensureUnusedCapacity(self: *Self, gpa: Allocator, additional_count: usize) Allocator.Error!void {
             return self.ensureTotalCapacity(gpa, self.len + additional_count);
         }
         /// Modify the array so that it can hold exactly `new_capacity` items.
         /// Invalidates pointers if additional memory is needed.
         /// `new_capacity` must be greater or equal to `len`.
-        pub fn setCapacity(self: *Self, gpa: Allocator, new_capacity: usize) !void {
+        pub fn setCapacity(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
             assert(new_capacity >= self.len);
             const new_bytes = try gpa.alignedAlloc(u8, .of(Elem), capacityInBytes(new_capacity));
             if (self.len == 0) {
 @@ -514,7 +559,7 @@ pub fn MultiArrayList(comptime T: type) type {
         /// Create a copy of this list with a new backing store,
         /// using the specified allocator.
-        pub fn clone(self: Self, gpa: Allocator) !Self {
+        pub fn clone(self: Self, gpa: Allocator) Allocator.Error!Self {
             var result = Self{};
             errdefer result.deinit(gpa);
             try result.ensureTotalCapacity(gpa, self.len);
 @@ -654,7 +699,7 @@ test "basic usage" {
         c: u8,
     };
-    var list = MultiArrayList(Foo){};
+    var list: MultiArrayList(Foo) = .empty;
     defer list.deinit(ally);
     try testing.expectEqual(@as(usize, 0), list.items(.a).len);
 @@ -667,7 +712,7 @@ test "basic usage" {
         .c = 'a',
     });
-    list.appendAssumeCapacity(.{
+    try list.appendBounded(.{
         .a = 2,
         .b = "zigzag",
         .c = 'b',
 @@ -725,6 +770,8 @@ test "basic usage" {
     try testing.expectEqualStrings("zigzag", list.items(.b)[1]);
     try testing.expectEqualStrings("fizzbuzz", list.items(.b)[2]);
+    try testing.expectError(error.OutOfMemory, list.addOneBounded());
     list.set(try list.addOne(ally), .{
         .a = 4,
         .b = "xnopyt",
 @@ -749,10 +796,10 @@ test "basic usage" {
 // function used the @reduce code path.
 test "regression test for @reduce bug" {
     const ally = testing.allocator;
-    var list = MultiArrayList(struct {
+    var list: MultiArrayList(struct {
         tag: std.zig.Token.Tag,
         start: u32,
-    }){};
+    }) = .empty;
     defer list.deinit(ally);
     try list.ensureTotalCapacity(ally, 20);
 @@ -832,7 +879,7 @@ test "ensure capacity on empty list" {
         b: u8,
     };
-    var list = MultiArrayList(Foo){};
+    var list: MultiArrayList(Foo) = .empty;
     defer list.deinit(ally);
     try list.ensureTotalCapacity(ally, 2);
 @@ -867,15 +914,25 @@ test "insert elements" {
         b: u32,
     };
-    var list = MultiArrayList(Foo){};
+    var list = try MultiArrayList(Foo).initCapacity(ally, 2);
     defer list.deinit(ally);
-    try list.insert(ally, 0, .{ .a = 1, .b = 2 });
+    try list.insertBounded(0, .{ .a = 1, .b = 2 });
-    try list.ensureUnusedCapacity(ally, 1);
     list.insertAssumeCapacity(1, .{ .a = 2, .b = 3 });
+    try list.insert(ally, 0, .{ .a = 3, .b = 4 });
+    try testing.expectEqualSlices(u8, &[_]u8{ 3, 1, 2 }, list.items(.a));
+    try testing.expectEqualSlices(u32, &[_]u32{ 4, 2, 3 }, list.items(.b));
+}
+test "initCapacity" {
+    const gpa = testing.allocator;
+    var list = try MultiArrayList(struct { a: u8, b: u32 }).initCapacity(gpa, 404);
+    defer list.deinit(gpa);
-    try testing.expectEqualSlices(u8, &[_]u8{ 1, 2 }, list.items(.a));
+    try testing.expectEqual(0, list.len);
-    try testing.expectEqualSlices(u32, &[_]u32{ 2, 3 }, list.items(.b));
+    try testing.expectEqual(404, list.capacity);
 }
 test "union" {
 @@ -886,7 +943,7 @@ test "union" {
         b: []const u8,
     };
-    var list = MultiArrayList(Foo){};
+    var list: MultiArrayList(Foo) = .empty;
     defer list.deinit(ally);
     try testing.expectEqual(@as(usize, 0), list.items(.tags).len);
 @@ -934,7 +991,7 @@ test "union" {
 }
 test "sorting a span" {
-    var list: MultiArrayList(struct { score: u32, chr: u8 }) = .{};
+    var list: MultiArrayList(struct { score: u32, chr: u8 }) = .empty;
     defer list.deinit(testing.allocator);
     try list.ensureTotalCapacity(testing.allocator, 42);
 @@ -981,7 +1038,7 @@ test "0 sized struct field" {
         b: f32,
     };
-    var list = MultiArrayList(Foo){};
+    var list: MultiArrayList(Foo) = .empty;
     defer list.deinit(ally);
     try testing.expectEqualSlices(u0, &[_]u0{}, list.items(.a));
 @@ -1007,7 +1064,7 @@ test "0 sized struct" {
         a: u0,
     };
-    var list = MultiArrayList(Foo){};
+    var list: MultiArrayList(Foo) = .empty;
     defer list.deinit(ally);
     try testing.expectEqualSlices(u0, &[_]u0{}, list.items(.a));