[Date Prev][Date Next][Thread Prev][Thread Next]
- Subject: Re: Dedicated error value/type for Lua?
- From: Mark Hamburg <mhamburg@...>
- Date: Tue, 21 Dec 2004 21:48:44 -0800
That is certainly the way to deal with this within Lua as it stands, but the
conventions used in FinalizedExceptions and for routines like io.open avoid
having a separate success code by overloading the first result.
on 12/21/04 9:10 PM, Rici Lake at firstname.lastname@example.org wrote:
> On 21-Dec-04, at 9:04 PM, Mark Hamburg wrote:
>> The following is a non-ideal example, but the idea is that if one
>> adopts the
>> convention that libraries should return errors rather than throwing
>> exceptions (see http://lua-users.org/wiki/FinalizedExceptions), then it
>> would help to have a way to express errors when false and nil are valid
> Surely the pcall convention (first result is the success indicator) does
> just that?
>> function itemExists( db, itemKey )
>> -- Returns true if database db contains an item with the
>> -- given key. Returns false if the database does not contain
>> -- an item with given key. Returns error in the event of an
>> -- error reading the database.
> Which this example is perfect for:
> true, true (or perhaps some more useful value)
> true, false -- no such key
> false, "Wrong password, bozo" -- database error
>> Example usage:
>> exists = error_assert( itemExists( db, itemKey ) )
> where error_assert is (in lua 5.1, I think):
> function (success, ...)
> if success then return ...
> else error((...))