Go Card Error Handling

[Mark Waddingham]

Hi all,

Whilst investigating a bug this afternoon 
(http://quality.livecode.com/show_bug.cgi?id=17873 - which has a moral 
attached to it, I'll come back to that) I was reminded that 'go card' 
seems to have somewhat inconsistent error handling compared to other 
commands which reference objects.

In pretty much all cases I can think of if a chunk cannot be resolved 
because one of its parts does not exist, then a runtime error is thrown. 
e.g.

    put the name of button "ThisButtonDoesNotExist"
    -- throws error "Chunk: no such object"

    copy char 1 to 5 of field 1 of card "ThisCardDoesNotExist"
    -- throws error "Chunk: can't find card"

However, if I do this:

    go card "ThisCardDoesNotExist"
    -- no error thrown: the result is "no such card"

In situations such as this, usually there is an apparent reason for the 
difference I can point to - however in this case I struggle to think of 
one. 'Going' to a card requires resolving a chunk reference, and by the 
rules which are followed everywhere (?) else, and so if that chunk 
reference does not resolve an error should be thrown.

I was just wondering if anyone knew why the behavior of 'go card' is 
different from, well, pretty much all other commands acting on chunks... 
Is it a HyperCard compatibility thing? An oversight from long ago? Is 
the difference actually useful and important in any way?

I filed an anomaly about it here - 
http://quality.livecode.com/show_bug.cgi?id=17901 - as it seems truly 
anomalous, however, like everything else, knowing the 'why it is the way 
it is' would be helpful to decide whether something should be done about 
it at some point, or whether it is something which should always be the 
way it currently is.

Warmest Regards,

Mark.

P.S. In regards to the original report which prompted my pondering on 
'go card', then its important to remember (when processing actual 
formatted text) that just because something looks like a space, it 
doesn't mean it is a space - spaces and non-breaking spaces are very 
different things (from the point of view of comparing strings, at 
least!).

-- 
Mark Waddingham ~ mark at livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps