USING syntax ? - help please ...

[Phil Hepburn]

Hi Guys,

Sorry, I must not have been paying attention at the Conference in Cologne, although I did learn a great deal (LOTS) ;-0) Thanks to all session providers.

Please can you put me right on the correct syntax to use for "begin/end USING", that we can now use like in C#.

I wish to have a StreamReader object which is opened then closed and removed within my IF statement - simple images attached of my so far fail attempts.

Please be aware that my brain is a bit fuddled as I have just spent a few hours coding Async/Await/Task samples. Much watch some cricket !

helpForum_using_01.png (10.99 KiB) Viewed 842 times

helpForum_using_02.png (10.74 KiB) Viewed 842 times

TIA,
Phil,
Wales, UK (at the moment )

[wriedmann]

Hi Phil,

this is my own sample for the using statement:

Code: Select all

using System.IO                              
using System.Text

function Start( ) as void                     
local cFileName as string
local aBytes as byte[]
	                         
cFileName := "c:tempUsing.txt"
System.Console.WriteLine("start working with" + cFileName )
begin using var oFile := FileStream{ cFileName, FileMode.OpenOrCreate, FileAccess.ReadWrite } // as FileStream
  aBytes := Encoding.ASCII.GetBytes( "Hello world!" )
  oFile:Write( aBytes, 0, aBytes:Length )
end using                                                
// file is not only out of scope, but also disposed, i.e. closed
System.Console.WriteLine("end working with" + cFileName )
System.Console.Write( "press a key...." )
System.Console.ReadKey()
	
return

I was not able to use the as FileStream in the using statement, only var worked.

Wolfgang

[FFF]

Hi Phil,
well, there IS a help file, even offline
From what i read:
BEGIN USING VAR oTest := Test{}
oTest:DoSomething()
END USING
....
Or, maybe i didn't understand the problem

BTW, i didn't find in help, how multiple vars are handled - if one has to nest them, or one "End Using" to unbound them all...

Karl

[wriedmann]

Hi Karl,

BTW, i didn't find in help, how multiple vars are handled - if one has to nest them, or one "End Using" to unbound them all...

Fabrice said you can nest them, and this is how it works also in C#.

Code: Select all

begin using var v1 := ...
  begin using var v2 := ....
    do something
  end using
end using

Wolfgang

[Phil Hepburn]

Hi Karl,

Yes, and I was using the on-line help from the web site / forum.

Problem with all new stuff however, is when is/was uploaded or added, etc., etc,.

The on-line details I found were the basis of my attempts, and what I posted to you guys.

Oh! - I see, there are at least two places in the on-line HELP which have different versions of syntax! Or there was a couple of hours ago. Now I see at least two versions of the same (and improved) syntax. Who has been busy this afternoon ? Can't now find the one with 'eos' and the ?s in my last images.

Fingers crossed that this now works.

Thanks Wolfgang for you sample.

Regards,
Phil.

[Phil Hepburn]

Karl (and all),

This is what I had previously found and tried to use and interpret.

helpForum_using_03.png (49.25 KiB) Viewed 842 times

This may be a correct and fuller way to define the syntax BUT, as a standard user guy I find it hard to understand.

HTH,
Phil

[wriedmann]

Hi Phil,

the problem with this documentation page is that it was auto-generated from the language definition, and someone from the devteam can explain what every word exactly means.

The word "eos" means "end of statement", I think.

To be sure, you could check also https://docs.xsharp.it where I had added exact the sample after I returned from the conference:

http://docs.xsharp.it/doku.php?id=using

I have to explain it better, I know - there needs to be said the used object must implement the IDisposable interface.

Wolfgang

[Phil Hepburn]

Wolfgang - Thanks, and that explains why I could not USE a 'StringBuilder' class / object ;-0((

helpForum_using_04.png (13.21 KiB) Viewed 842 times

That is a shame.

Are there any other restrictions as to what the USING class can or can't be ?

Cheers,
Phil.

[wriedmann]

Hi Phil,

since the X# compiler is using the Roslyn compiler, this is true also for C#. So the X# team is not to blame for this:

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-statement

Wolfgang

[Chris]

Guys,

Well, what BEGIN USING does is to implicitly call Dispose() on the object after it is used, so if the class does not implement IDisposable (which provides the Dispose() method) then it wouldn't make much sense

OK, it actually also implicitly uses a TRY...FINALLY block and enforces a limited scope (when exiting it, it can now be collected) for the declared variable(s), which you can also enforce manually if you want, for any local, no matter if it is an IDisposable or not, by using BEGIN..END SCOPE:

Code: Select all

BEGIN SCOPE
  // All vars declared here will be visible only inside this block (scope)
  LOCAL oAnyVar AS MyType
  // ...
END SCOPE

Chris