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Merge pull request #15134 from castholm/reverse-iterator

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std.mem.reverseIterator: misc improvements
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Veikka Tuominen 2023-04-02 18:06:55 +03:00 committed by GitHub
commit a31450375e
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1 changed files with 81 additions and 26 deletions
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107
lib/std/mem.zig
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@ -2989,52 +2989,107 @@ test "reverse" {
}
fn ReverseIterator(comptime T: type) type {
const info: struct { Child: type, Pointer: type } = blk: {
const Pointer = blk: {
switch (@typeInfo(T)) {
.Pointer => |info| switch (info.size) {
.Slice => break :blk .{
.Child = info.child,
.Pointer = @Type(.{ .Pointer = .{
.size = .Many,
.is_const = info.is_const,
.is_volatile = info.is_volatile,
.alignment = info.alignment,
.address_space = info.address_space,
.child = info.child,
.is_allowzero = info.is_allowzero,
.sentinel = info.sentinel,
} }),
.Pointer => |ptr_info| switch (ptr_info.size) {
.One => switch (@typeInfo(ptr_info.child)) {
.Array => |array_info| {
var new_ptr_info = ptr_info;
new_ptr_info.size = .Many;
new_ptr_info.child = array_info.child;
new_ptr_info.sentinel = array_info.sentinel;
break :blk @Type(.{ .Pointer = new_ptr_info });
},
else => {},
},
.Slice => {
var new_ptr_info = ptr_info;
new_ptr_info.size = .Many;
break :blk @Type(.{ .Pointer = new_ptr_info });
},
else => {},
},
else => {},
}
@compileError("reverse iterator expects slice, found " ++ @typeName(T));
@compileError("expected slice or pointer to array, found '" ++ @typeName(T) ++ "'");
};
const Element = std.meta.Elem(Pointer);
const ElementPointer = @TypeOf(&@as(Pointer, undefined)[0]);
return struct {
ptr: info.Pointer,
ptr: Pointer,
index: usize,
pub fn next(self: *@This()) ?info.Child {
pub fn next(self: *@This()) ?Element {
if (self.index == 0) return null;
self.index -= 1;
return self.ptr[self.index];
}
pub fn nextPtr(self: *@This()) ?ElementPointer {
if (self.index == 0) return null;
self.index -= 1;
return &self.ptr[self.index];
}
};
}
/// Iterate over a slice in reverse.
/// Iterates over a slice in reverse.
pub fn reverseIterator(slice: anytype) ReverseIterator(@TypeOf(slice)) {
return .{ .ptr = slice.ptr, .index = slice.len };
const T = @TypeOf(slice);
if (comptime trait.isPtrTo(.Array)(T)) {
return .{ .ptr = slice, .index = slice.len };
} else {
comptime assert(trait.isSlice(T));
return .{ .ptr = slice.ptr, .index = slice.len };
}
}
test "reverseIterator" {
const slice: []const i32 = &[_]i32{ 5, 3, 1, 2 };
var it = reverseIterator(slice);
try testing.expectEqual(@as(?i32, 2), it.next());
try testing.expectEqual(@as(?i32, 1), it.next());
try testing.expectEqual(@as(?i32, 3), it.next());
try testing.expectEqual(@as(?i32, 5), it.next());
try testing.expectEqual(@as(?i32, null), it.next());
{
var it = reverseIterator("abc");
try testing.expectEqual(@as(?u8, 'c'), it.next());
try testing.expectEqual(@as(?u8, 'b'), it.next());
try testing.expectEqual(@as(?u8, 'a'), it.next());
try testing.expectEqual(@as(?u8, null), it.next());
}
{
var array = [2]i32{ 3, 7 };
const slice: []const i32 = &array;
var it = reverseIterator(slice);
try testing.expectEqual(@as(?i32, 7), it.next());
try testing.expectEqual(@as(?i32, 3), it.next());
try testing.expectEqual(@as(?i32, null), it.next());
it = reverseIterator(slice);
try testing.expect(trait.isConstPtr(@TypeOf(it.nextPtr().?)));
try testing.expectEqual(@as(?i32, 7), it.nextPtr().?.*);
try testing.expectEqual(@as(?i32, 3), it.nextPtr().?.*);
try testing.expectEqual(@as(?*const i32, null), it.nextPtr());
var mut_slice: []i32 = &array;
var mut_it = reverseIterator(mut_slice);
mut_it.nextPtr().?.* += 1;
mut_it.nextPtr().?.* += 2;
try testing.expectEqual([2]i32{ 5, 8 }, array);
}
{
var array = [2]i32{ 3, 7 };
const ptr_to_array: *const [2]i32 = &array;
var it = reverseIterator(ptr_to_array);
try testing.expectEqual(@as(?i32, 7), it.next());
try testing.expectEqual(@as(?i32, 3), it.next());
try testing.expectEqual(@as(?i32, null), it.next());
it = reverseIterator(ptr_to_array);
try testing.expect(trait.isConstPtr(@TypeOf(it.nextPtr().?)));
try testing.expectEqual(@as(?i32, 7), it.nextPtr().?.*);
try testing.expectEqual(@as(?i32, 3), it.nextPtr().?.*);
try testing.expectEqual(@as(?*const i32, null), it.nextPtr());
var mut_ptr_to_array: *[2]i32 = &array;
var mut_it = reverseIterator(mut_ptr_to_array);
mut_it.nextPtr().?.* += 1;
mut_it.nextPtr().?.* += 2;
try testing.expectEqual([2]i32{ 5, 8 }, array);
}
}
/// In-place rotation of the values in an array ([0 1 2 3] becomes [1 2 3 0] if we rotate by 1)