Re: FLASH: Eval or not to Eval

[John Dowdell]

At 6:40 AM 8/7/0, Stuart Mayhew (Garanti Teknoloji) wrote:

> I am hoping that somebody in a clear and concise manner can

> explain the purpose and function of the Eval function in

> the action script editor.


It's similar to the "eval" function in JavaScript...?  ;-)


Seriously, this is always a tricky thing to describe with words... the

shortest explanation I've seen is that it's a way to "de-string-ify"

variables, a way to turn strings into commands.


For instance, compare these two phrases:

"You're feeling very sleepy... your eyes are getting heavy."

"It's possible to remember a feeling of great ease, and comfort... you

might even notice a warmth, and heaviness, as you go deeper, and deeper."


The first is a command, while the second... hey, hold it, where did that

example come from, it's too oblique, let me try again... "the map is not

the territory"? no, get it into computery terms.... ;-)



Suppose you've named a variable customer23, then you wish to loop through a

series of related customer names like this (pseudo-script):


   with i = 1 to numCustomers

     thisCustomer = "customer" & i

     CalculateBill( thisCustomer )

   end loop


The "thisCustomer" reference would actually be a changing *string* here,

not a changing variable name. You'd want to de-string-ify that name to get

an actual object reference, and this is where functions like "eval" or

"value" can help. (Some languages also have a "do" or "execute" command,

which interprets a string as a literal command.)



I'm sorry that this description seems self-referential... part of the

problem is that eval's functionality is itself abstract, turning an

indirect reference to a direct reference. Does the above help at all...?


jd










John Dowdell, Macromedia Tech Support, San Francisco CA US

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