RE: [flexcoders] Method variable scoping problem with Flex compiler
Fact of life with ECMAScript (hence, with ActionScript as well).
Take a look at the language specification itself for details, but locals in
your example are scoped to the function, not to code blocks within the function
delimited by braces. Yes, this differs from C-based languages, and as someone
who regularly works in both I've been bitten by this more than once as well.
Best,
Seth
From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of
toofah_gm
Sent: Thursday, December 04, 2008 2:32 PM
To: flexcoders@yahoogroups.com
Subject: [flexcoders] Method variable scoping problem with Flex compiler
I came across another scoping issue today that scared me. I sure wish
that the scoping in the ActionScript language worked the same way C++,
C#, Java, and others work!
Here's the code:
for each (var o:Object in myArray)
{
var myProblemObject:ProblemObject;
if (some condition)
{
myProblemObject = new ProblemObject();
... more code here ...
}
... still more code here...
if (myProblemObject)
{
... do some stuff ...
}
}
In this code myProblemObject is NULL when things start out...great!
The problem comes after an instance of myProblemObject gets created.
Every time through the loop after this myProblemObject is no longer
NULL. This is not consistent with any other language that I have
worked with and is therefore not obvious to the developer working with
the code.
Why is myProblemObject not reset each time through the loop? It is a
variable declaration.
Gary
--- In flexcoders@yahoogroups.com, toofah_gm [EMAIL PROTECTED] wrote:
It seems to me and my co-workers that the Flex compiler is broken
when
it comes to local variable scoping within methods.
For example:
for (var i:int=0; icount; i++)
{
// do something
}
for (var i:int=0; icount; i++)
{
// do something else
}
This gives a compiler warning stating that 'i' is already defined.
But in every other language that I have used, this is completely
valid. Yes 'i' was defined above, but 'i' should only be scoped
within the 'for' loop and should be invalid outside of it.
Another example:
if (x)
{
var myArray:Array = new Array();
// do more stuff
}
myArray.push(some data);
This one compiles, when I believe that it shouldn't. myArray should
only be defined within the 'if' statement. If you don't go into the
'if' statement you have a problem here.
Does anyone understand why the Flex compiler allows this? Is this
just a BUG with the compiler?
Anyway, this is just driving me a little crazy. ;)
Gary
Re: [flexcoders] Method variable scoping problem with Flex compiler
*Why* it's different I can't tell you, but if you're being regularly
surprised, it sounds like you might benefit from skimming through the
language reference. This behavior is described on the
Variableshttp://livedocs.adobe.com/flex/3/html/help.html?content=03_Language_and_Syntax_07.html#118946page
of help resource center, under 'Understanding variable scope'.
From there (this may scare you even more!):
*ActionScript variables, unlike variables in C++ and Java, do not have
block-level scope. ... An interesting implication of the lack of block-level
scope is that you can read or write to a variable before it is declared, as
long as it is declared before the function ends. This is because of a
technique called hoisting, which means that the compiler moves all variable
declarations to the top of the function.*
On Thu, Dec 4, 2008 at 5:31 PM, toofah_gm [EMAIL PROTECTED] wrote:
I came across another scoping issue today that scared me. I sure wish
that the scoping in the ActionScript language worked the same way C++,
C#, Java, and others work!
Here's the code:
for each (var o:Object in myArray)
{
var myProblemObject:ProblemObject;
if (some condition)
{
myProblemObject = new ProblemObject();
... more code here ...
}
... still more code here...
if (myProblemObject)
{
... do some stuff ...
}
}
In this code myProblemObject is NULL when things start out...great!
The problem comes after an instance of myProblemObject gets created.
Every time through the loop after this myProblemObject is no longer
NULL. This is not consistent with any other language that I have
worked with and is therefore not obvious to the developer working with
the code.
Why is myProblemObject not reset each time through the loop? It is a
variable declaration.
Gary
--- In flexcoders@yahoogroups.com flexcoders%40yahoogroups.com,
toofah_gm [EMAIL PROTECTED] wrote:
It seems to me and my co-workers that the Flex compiler is broken
when
it comes to local variable scoping within methods.
For example:
for (var i:int=0; icount; i++)
{
// do something
}
for (var i:int=0; icount; i++)
{
// do something else
}
This gives a compiler warning stating that 'i' is already defined.
But in every other language that I have used, this is completely
valid. Yes 'i' was defined above, but 'i' should only be scoped
within the 'for' loop and should be invalid outside of it.
Another example:
if (x)
{
var myArray:Array = new Array();
// do more stuff
}
myArray.push(some data);
This one compiles, when I believe that it shouldn't. myArray should
only be defined within the 'if' statement. If you don't go into the
'if' statement you have a problem here.
Does anyone understand why the Flex compiler allows this? Is this
just a BUG with the compiler?
Anyway, this is just driving me a little crazy. ;)
Gary
Re: [flexcoders] Method variable scoping problem with Flex compiler
AFAIK, It's different because that's the way it works in LISP by way of
Scheme, JavaScript, and ECMAScript.
-Josh
On Fri, Dec 5, 2008 at 12:15 PM, Michael Prescott
[EMAIL PROTECTED] wrote:
*Why* it's different I can't tell you, but if you're being regularly
surprised, it sounds like you might benefit from skimming through the
language reference. This behavior is described on the
Variableshttp://livedocs.adobe.com/flex/3/html/help.html?content=03_Language_and_Syntax_07.html#118946page
of help resource center, under 'Understanding variable scope'.
From there (this may scare you even more!):
*ActionScript variables, unlike variables in C++ and Java, do not have
block-level scope. ... An interesting implication of the lack of block-level
scope is that you can read or write to a variable before it is declared, as
long as it is declared before the function ends. This is because of a
technique called hoisting, which means that the compiler moves all variable
declarations to the top of the function.*
On Thu, Dec 4, 2008 at 5:31 PM, toofah_gm [EMAIL PROTECTED] wrote:
I came across another scoping issue today that scared me. I sure wish
that the scoping in the ActionScript language worked the same way C++,
C#, Java, and others work!
Here's the code:
for each (var o:Object in myArray)
{
var myProblemObject:ProblemObject;
if (some condition)
{
myProblemObject = new ProblemObject();
... more code here ...
}
... still more code here...
if (myProblemObject)
{
... do some stuff ...
}
}
In this code myProblemObject is NULL when things start out...great!
The problem comes after an instance of myProblemObject gets created.
Every time through the loop after this myProblemObject is no longer
NULL. This is not consistent with any other language that I have
worked with and is therefore not obvious to the developer working with
the code.
Why is myProblemObject not reset each time through the loop? It is a
variable declaration.
Gary
--- In flexcoders@yahoogroups.com flexcoders%40yahoogroups.com,
toofah_gm [EMAIL PROTECTED] wrote:
It seems to me and my co-workers that the Flex compiler is broken
when
it comes to local variable scoping within methods.
For example:
for (var i:int=0; icount; i++)
{
// do something
}
for (var i:int=0; icount; i++)
{
// do something else
}
This gives a compiler warning stating that 'i' is already defined.
But in every other language that I have used, this is completely
valid. Yes 'i' was defined above, but 'i' should only be scoped
within the 'for' loop and should be invalid outside of it.
Another example:
if (x)
{
var myArray:Array = new Array();
// do more stuff
}
myArray.push(some data);
This one compiles, when I believe that it shouldn't. myArray should
only be defined within the 'if' statement. If you don't go into the
'if' statement you have a problem here.
Does anyone understand why the Flex compiler allows this? Is this
just a BUG with the compiler?
Anyway, this is just driving me a little crazy. ;)
Gary
--
Therefore, send not to know For whom the bell tolls. It tolls for thee.
Like the cut of my jib? Check out my Flex blog!
:: Josh 'G-Funk' McDonald
:: 0437 221 380 :: [EMAIL PROTECTED]
:: http://flex.joshmcdonald.info/
:: http://twitter.com/sophistifunk
Re: [flexcoders] Method variable scoping problem with Flex compiler
This is variable hoisting in action:
http://docs.huihoo.com/web/js/es4/core/definitions.html#hoist
I can't really find a clearer explanation, but the gist of it is that
variable definitions are sometimes moved to the parent block, and
sometimes this results in the sort of weird behavior you're seeing.
That's the how, but I don't really know the why--anyone more savvy about
hoisting care to enlighten the list?
--
Maciek Sakrejda
Truviso, Inc.
http://www.truviso.com
-Original Message-
From: toofah_gm [EMAIL PROTECTED]
Reply-To: flexcoders@yahoogroups.com
To: flexcoders@yahoogroups.com
Subject: [flexcoders] Method variable scoping problem with Flex compiler
Date: Fri, 15 Aug 2008 19:43:09 -
It seems to me and my co-workers that the Flex compiler is broken when
it comes to local variable scoping within methods.
For example:
for (var i:int=0; icount; i++)
{
// do something
}
for (var i:int=0; icount; i++)
{
// do something else
}
This gives a compiler warning stating that 'i' is already defined.
But in every other language that I have used, this is completely
valid. Yes 'i' was defined above, but 'i' should only be scoped
within the 'for' loop and should be invalid outside of it.
Another example:
if (x)
{
var myArray:Array = new Array();
// do more stuff
}
myArray.push(some data);
This one compiles, when I believe that it shouldn't. myArray should
only be defined within the 'if' statement. If you don't go into the
'if' statement you have a problem here.
Does anyone understand why the Flex compiler allows this? Is this
just a BUG with the compiler?
Anyway, this is just driving me a little crazy. ;)
Gary
RE: [flexcoders] Method variable scoping problem with Flex compiler
Not sometimes. Local vars are always hoisted from the block where they
are declared to the scope of the entire function.
As Ecmascript requires! : )
Gordon Smith
Adobe Flex SDK Team
From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On
Behalf Of Maciek Sakrejda
Sent: Friday, August 15, 2008 12:54 PM
To: flexcoders@yahoogroups.com
Subject: Re: [flexcoders] Method variable scoping problem with Flex
compiler
This is variable hoisting in action:
http://docs.huihoo.com/web/js/es4/core/definitions.html#hoist
http://docs.huihoo.com/web/js/es4/core/definitions.html#hoist
I can't really find a clearer explanation, but the gist of it is that
variable definitions are sometimes moved to the parent block, and
sometimes this results in the sort of weird behavior you're seeing.
That's the how, but I don't really know the why--anyone more savvy about
hoisting care to enlighten the list?
--
Maciek Sakrejda
Truviso, Inc.
http://www.truviso.com http://www.truviso.com
-Original Message-
From: toofah_gm [EMAIL PROTECTED] mailto:garym%40byu.edu
Reply-To: flexcoders@yahoogroups.com
mailto:flexcoders%40yahoogroups.com
To: flexcoders@yahoogroups.com mailto:flexcoders%40yahoogroups.com
Subject: [flexcoders] Method variable scoping problem with Flex compiler
Date: Fri, 15 Aug 2008 19:43:09 -
It seems to me and my co-workers that the Flex compiler is broken when
it comes to local variable scoping within methods.
For example:
for (var i:int=0; icount; i++)
{
// do something
}
for (var i:int=0; icount; i++)
{
// do something else
}
This gives a compiler warning stating that 'i' is already defined.
But in every other language that I have used, this is completely
valid. Yes 'i' was defined above, but 'i' should only be scoped
within the 'for' loop and should be invalid outside of it.
Another example:
if (x)
{
var myArray:Array = new Array();
// do more stuff
}
myArray.push(some data);
This one compiles, when I believe that it shouldn't. myArray should
only be defined within the 'if' statement. If you don't go into the
'if' statement you have a problem here.
Does anyone understand why the Flex compiler allows this? Is this
just a BUG with the compiler?
Anyway, this is just driving me a little crazy. ;)
Gary
