ensureTotalCapacityPrecise

        pub fn ensureTotalCapacityPrecise(self: *Self, new_capacity: usize) Allocator.Error!void {
            if (@sizeOf(T) == 0) {
                self.capacity = math.maxInt(usize);
                return;
            }

            if (self.capacity >= new_capacity) return;
            self.pointer_stability.assertUnlocked();
            // Here we avoid copying allocated but unused bytes by
            // attempting a remap, 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 (self.allocator.remap(old_memory, new_capacity)) |new_memory| {
                self.items.ptr = new_memory.ptr;
                self.capacity = new_memory.len;
            } else {
                const new_memory = try self.allocator.alignedAlloc(T, alignment, new_capacity);
                @memcpy(new_memory[0..self.items.len], self.items);
                self.allocator.free(old_memory);
                self.items.ptr = new_memory.ptr;
                self.capacity = new_memory.len;
            }
        }