VariableNameIterator

    pub const VariableNameIterator = struct {
        pub const NextSizeError = uefi.UnexpectedError || error{
            DeviceError,
            Unsupported,
        };

        pub const IterateVariableNameError = NextSizeError || error{
            BufferTooSmall,
        };

        services: *const RuntimeServices,
        buffer: []u16,
        guid: Guid,

        pub fn nextSize(self: *VariableNameIterator) NextSizeError!?usize {
            var len: usize = 0;
            switch (self.services._getNextVariableName(
                &len,
                null,
                &self.guid,
            )) {
                .buffer_too_small => return len,
                .not_found => return null,
                .device_error => return error.DeviceError,
                .unsupported => return error.Unsupported,
                else => |status| return uefi.unexpectedStatus(status),
            }
        }

        /// Call `nextSize` to get the length of the next variable name and check
        /// if `buffer` is large enough to hold the name.
        pub fn next(
            self: *VariableNameIterator,
        ) IterateVariableNameError!?[:0]const u16 {
            var len = self.buffer.len;
            switch (self.services._getNextVariableName(
                &len,
                @ptrCast(self.buffer.ptr),
                &self.guid,
            )) {
                .success => return self.buffer[0 .. len - 1 :0],
                .not_found => return null,
                .buffer_too_small => return error.BufferTooSmall,
                .device_error => return error.DeviceError,
                .unsupported => return error.Unsupported,
                else => |status| return uefi.unexpectedStatus(status),
            }
        }
    }