Re: Odd behaviour with multiple return values and varargs

["Aaron Brown" <arundelo@...>]

Jerome Vuarand wrote:

> So far the only real argument in favor of truncation on
> that discussion is that it's an implementation limitation.
> All other arguments are either irrelevant (a matter of
> personnal preference) or applicable to the last argument
> too.

Forgive me for quoting myself, but in Kurt's and my book
(page 80) I wrote:

> This rule (adjust every expression except the last to one
> value) may seem more complicated than necessary, but there
> is good reasoning behind it.  If every expression in a
> value list were adjusted to one value, there would need to
> be a special way to override this, which would make the
> ability of Lua functions to return multiple values harder
> to use.  If no expressions in a value list were adjusted
> to one value, then any function returning less or more
> than one value would throw off the positioning of
> everything that came after it in the value list.

Take the following statement:

 Foo(Bar(), Baz(), Quux())

In that statement, Quux() returning more than one value when
you think it returns one is only a problem if Foo() takes
more arguments than you think it does.  In a stipulated Lua
that doesn't adjust return values, Bar() and Baz() returning
more or less than one value when you think they return one
would always be a problem, because it would throw off the
alignment of the remaining arguments.  (Similar reasoning
applies to multiple assignment or table constructors.)

I think Lua's actual behavior is a good middle road between
making multiple returns hard to use and making them a
too-fertile source of bugs.

--
Aaron
http://arundelo.com/