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Simplify std.ArrayList.replaceRange and std.ArrayList.replaceRangeAssumeCapacity (#31710)

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The implementations of `std.ArrayList.replaceRange` and `std.ArrayList.replaceRangeAssumeCapacity` were needlessly complicated, called `@memcpy` too many times, and left the structure in a semi-modified state in OOM conditions. This commit fixes that.

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31710
Reviewed-by: Andrew Kelley <andrew@ziglang.org>
Co-authored-by: Hila Friedman <red.black.liquorice@gmail.com>
Co-committed-by: Hila Friedman <red.black.liquorice@gmail.com>
This commit is contained in:
Hila Friedman
2026-04-02 15:11:24 +02:00
committed by Andrew Kelley
parent f4eecf8d7d
commit 746dd51faf
1 changed files with 21 additions and 30 deletions
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lib/std/array_list.zig
+21 -30
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@@ -857,16 +857,8 @@ pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
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);
}
try self.ensureTotalCapacity(gpa, try addOrOom(self.items.len - len, new_items.len));
self.replaceRangeAssumeCapacity(start, len, new_items);
}
/// Grows or shrinks the list as necessary.
@@ -874,26 +866,20 @@ pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
/// 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];
pub fn replaceRangeAssumeCapacity(
self: *Self,
start: usize,
len: usize,
new_items: []const T,
) void {
std.debug.assert(self.capacity - self.items.len >= new_items.len -| len);
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;
}
const tail = self.items[start + len ..];
const vacated = self.items[self.items.len - (len -| new_items.len) ..];
self.items.len = self.items.len - len + new_items.len;
@memmove(self.items[start + new_items.len ..], tail);
@memcpy(self.items[start..][0..new_items.len], new_items);
@memset(vacated, undefined);
}
/// Grows or shrinks the list as necessary.
@@ -902,7 +888,12 @@ pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
///
/// 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 {
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);
}