On Jul 8, 2011, at 9:46 AM, Bob Sneidar wrote:
Ic. Well if it worked that way, then there would be no point in
declaring it's scope (forgive me if that is not the right term) to
begin with, as all variables would only have one "scope" that being
global. Maybe I'm not getting it.
Bob
Here is a detailed description that most people won't care to read,
but you asked, so here goes :-)
There are many scopes that you can create.
When declaring a global, you are defining that variable as belonging
to Livecode (if in the development environment) or the standalone app.
The programming rule should be that you don't want to create the
ambiguity that let's the script engine decide which scope you mean.
Since it is very easy to accidentally use the same name for variables
in different namespaces, it far better to avoid this by being
disciplined in your coding. This is true in any programming language.
If it helps, think of namespaces as separate tables on a spreadsheet.
One table is named
global variables of this app (either LC or a standalone)
-- eg gCupHolder, gDateString, gUserName
script locals of the SCRIPT of button "Run This" of card 2 of this
stack
-- pathNamesArray, repeatLoopCount, currHilitedLine
script locals of the SCRIPT of card "January Data" of this stack
-- accountingSummary, currentMonth
local variables of the HANDLER "processData" of the script of this
stack
-- loopCounter, shortCardId, imgID
local variables of the HANDLER "getDateAsJulian" of the script of
card 5 of this substack
-- loopCounter, shortCardId, imgID
Each of these 'tables' or namespaces can have a variable named
'cupHolder' and it can have different contents. LC is most capable of
keeping all of these accurate, neat, and tidy... but there are rules.
To access a LC global or an operating system global (those starting
with $ such as $USER $HOME $SHELL ) you need to use
global gCupHolder,
in the script container before using these in your script
(but you don't have to declare the $USER or $HOME since they
can only be system globals)
A global can be declared but if is is not used, the Variable Watcher
will not show it.
Once it is used by any script, it gets created ( if it does not exist)
and is global to any scripts that run in that environment. The
scripting you write must declare that you want to access the global
namespace.
-- options for declaring are ---
*1* as a top line in a script
*2* as a line in the script container that is not in a handler or
function
{handlers in this container}
global cupHolder
on processData
...
end processData
*3* as a line inside a handler, but before the first time you use it
in that handler
-- note: avoid global cupHolder inside a repeat loop
on processData
global cupHolder
end processData
--------------------------
to use cupHolder as a SCRIPT local scope variable use
local cupHolder
at the top of a script container
--------------------------
to use cupHolder as a HANDLER local scope variable use
any statement to create the variable
eg
on processData
put "morning coffee" into cupHolder
*4* in the message box
typing "global gAAA" will create this global name for all stacks and
scripts
NOTE: The message box can access globals without declaring them
first... just refer to them
eg.. put gCupHolder & the seconds
-----
The programming rule should be that you don't want to create the
ambiguity that let's the script engine decide which scope you mean.
Since it is very easy to accidentally use the same name for variables
in different namespaces, it far better to avoid this by being
disciplined in your coding. This gets much trickier if you pass
parameters and try to use those names as well.
on processData monthlyTotals, workerHours, officeCode, cupHolder
-- now these 4 parameters are HANDLER locals and will vanish at the
end of this handler
end processData
Hope this helps you figure it out.
Jim Ault
Las Vegas
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