Dim Byref syntax

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dkl
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Location: Germany

Dim Byref syntax

Postby dkl » May 16, 2015 16:27

Hi,

recently I started some work on adding support for Dim'ing references (Type &name in C++), because I think it'd be nice to have this not just for Byref parameters, but also local variables and Type fields.

I started with this syntax idea:

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dim i as integer
dim byref ri as integer = i  '' ri is an "alias" for i

dim byref r1 as integer = i, byref r2 as integer = i

dim byref as integer r1 = i, r2 = i, r3 = i

var byref ri = i


What do you think about the syntax? I like it because it matches the syntax for Byref parameters, and Byref function results, and it doesn't require a new keyword...

A possible alternative that I saw suggested on this forum a while ago, by adding the Ref keyword:

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dim ri as integer ref = i
dim as integer ref ri = i
var ref ri = i '' maybe a little odd? I like "var byref" better
fxm
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Re: Dim Byref syntax

Postby fxm » May 16, 2015 16:33

I prefer the syntax with which you started!
stylin
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Joined: Nov 06, 2005 5:19

Re: Dim Byref syntax

Postby stylin » May 16, 2015 17:28

I like the first syntax as well, very excited to see the development of this. :)
VANYA
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Re: Dim Byref syntax

Postby VANYA » May 16, 2015 18:05

With Byref better.
grindstone
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Location: Germany

Re: Dim Byref syntax

Postby grindstone » May 16, 2015 21:03

Hello,

I don't understand which effect this should have. Would

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dim i as integer
dim byref ri as integer = i  '' ri is an "alias" for i

be the same as

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dim i as integer
dim ri as integer ptr = @i
?

Greetings
grindstone
dafhi
Posts: 1241
Joined: Jun 04, 2005 9:51

Re: Dim Byref syntax

Postby dafhi » May 16, 2015 21:14

interesting concept!

i think i'd prefer "dim as byref integer"
fxm
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Location: Paris suburbs, FRANCE

Re: Dim Byref syntax

Postby fxm » May 16, 2015 22:18

A reference can be thought of as a constant pointer with automatic dereferencing (the compiler will apply the '*' operator for you).
You must think of 'ri' as a macro for '(*p)', where 'p' is a const pointer to 'i'.

That's like if you code this:

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#macro DimByRef (typename, ref, obj)
  Dim As typename Const Ptr ptr##ref = @(obj)
  #Define ref (*ptr##ref)
#endmacro
#macro VarByRef (ref, obj)
  Var ptr##ref = Cptr(Typeof(obj) Const Ptr, @(obj))
  #Define ref (*ptr##ref)
#endmacro


Dim As Integer i = 123

''Dim Byref As Integer ri = i
  DimByRef(Integer, ri, i)

Print ri
ri = 456
Print i


[edit]
better equivalent code
Last edited by fxm on May 18, 2015 16:42, edited 5 times in total.
grindstone
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Location: Germany

Re: Dim Byref syntax

Postby grindstone » May 16, 2015 23:58

Yes, I see, the effect is that i and ri will always return the same value, no matter which of them you change. It surely works fine, but I can't see any practical benefit. In the bottom line it only means that the same variable can be accessed by two (or more) different names.
stylin
Posts: 1253
Joined: Nov 06, 2005 5:19

Re: Dim Byref syntax

Postby stylin » May 17, 2015 0:30

@grindstone Hi, it would not only alias named objects, but also things like,

dim byref i as integer = *(some_complex_pointer_math)

Other than superficial syntactic sugar, references give you a few guarantees that pointers don't:
  • You're dealing with an actual object. Pointers can be invalid.
  • You're dealing with a single object. It's not immediately clear whether a pointer points to an array or not.
Basically, you have the same practical benefits as passing by reference to a procedure.
fxm
Posts: 9084
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Location: Paris suburbs, FRANCE

Re: Dim Byref syntax

Postby fxm » May 17, 2015 6:07

Two other examples (see also my previous post):

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#macro DimByRef (typename, ref, obj)
  Dim As typename Const Ptr ptr##ref = @(obj)
  #Define ref (*ptr##ref)
#endmacro
#macro VarByRef (ref, obj)
  Var ptr##ref = Cptr(Typeof(obj) Const Ptr, @(obj))
  #Define ref (*ptr##ref)
#endmacro


Dim As Integer I = 123

Dim As Integer CI = I
''Dim Byref As Integer RI = I
  DimByRef(Integer, RI, I)

Print I, CI, RI
CI = 456
Print I, CI, RI
RI = 789
Print I, CI, RI
Print

'------------------------------------------------------------------

''Var Byref RNI = *New Integer(1234)
  VarByRef(RNI, *New Integer(1234))

Print RNI
RNI = 5678
Print RNI
Delete @RNI

Sleep

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 123           123           123
 123           456           123
 789           456           789

 1234
 5678

- First example:
'CI' is a copy of 'I' ('@CI <> @I')
'RI' is a reference of 'I' ('@RI = @I')

- Second example:
'RNI' is the only reference of the "new" integer
Last edited by fxm on Mar 31, 2016 12:56, edited 5 times in total.
grindstone
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Location: Germany

Re: Dim Byref syntax

Postby grindstone » May 17, 2015 8:09

Thanks, I think I've got it now. But that means (if I understood it right), there can only be Dim'd a reference to a variable that already exists. In this case it's needless to mention the type, for it's already defined. I suggest the syntax should be similar to the 'SizeOf' statement, something like:

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Dim ri As RefTo(i)
marpon
Posts: 338
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Location: Paris - France

Re: Dim Byref syntax

Postby marpon » May 17, 2015 8:19

Hi
I aggree with that :
dim i as integer
dim byref ri as integer = i '' ri is an "alias" for i

be the same as

dim i as integer
dim ri as integer ptr = @i


I think in fact better with ptr ( that explain really it's a pointer), an for me (sorry if i don't understand ) it's not really needed.
Adding complexity to the compiler , is always risk for bugs , regression... , so better to select the extensions on not previously covered features, if is some bug is much more acceptable on new features than on previously existing ones.
( I have in mind the Line Input # ... that made me crazy ,until i understood it was a bug)

I would be much more interrested on addition of very efficient native string functions , such : replace , remove, split ... as discussed on previous post, it is a lot of posts around these kind of functions
fxm
Posts: 9084
Joined: Apr 22, 2009 12:46
Location: Paris suburbs, FRANCE

Re: Dim Byref syntax

Postby fxm » May 17, 2015 8:26

grindstone wrote:But that means (if I understood it right), there can only be Dim'd a reference to a variable that already exists. In this case it's needless to mention the type

I think with 'Dim Byref R As DataType = ...', we will could define a compatible type reference of an object!
(as we already can do it for parameters passed by reference and for functions returning by reference, with same compatibility rules than with their pointers)
Last edited by fxm on May 21, 2015 11:26, edited 2 times in total.
fxm
Posts: 9084
Joined: Apr 22, 2009 12:46
Location: Paris suburbs, FRANCE

Re: Dim Byref syntax

Postby fxm » May 17, 2015 9:57

marpon wrote:I think in fact better with ptr ( that explain really it's a pointer), an for me (sorry if i don't understand ) it's not really needed.

Simplification of expression compared to pointer (avoid to use operator '@' and especially '*'):

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#macro DimByRef (typename, ref, obj)
  Dim As typename Const Ptr ptr##ref = @(obj)
  #Define ref (*ptr##ref)
#endmacro
#macro VarByRef (ref, obj)
  Var ptr##ref = Cptr(Typeof(obj) Const Ptr, @(obj))
  #Define ref (*ptr##ref)
#endmacro

Dim As Zstring Ptr pz = @"FreeBASIC Zstring Ptr"
Print *pz
*pz &= " 1.2.1"
Print *pz
Print

''Dim Byref As Zstring rz = "FreeBASIC Zstring Ref"
  DimByRef(Zstring, rz, "FreeBASIC Zstring Ref")
Print rz
rz &= " 1.3.0"
Print rz

Sleep

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FreeBASIC Zstring Ptr
FreeBASIC Zstring Ptr 1.2.1

FreeBASIC Zstring Ref
FreeBASIC Zstring Ref 1.3.0
Last edited by fxm on May 18, 2015 16:43, edited 2 times in total.
D.J.Peters
Posts: 7780
Joined: May 28, 2005 3:28

Re: Dim Byref syntax

Postby D.J.Peters » May 17, 2015 14:04

I wonder me that the byref stuff is on the to do list.

Some of us waiting years of much more important things.

Joshy

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SCREENRES w,h,d,,FB.GFX_RESIZEABLE
' or
SCREENCONTROL SET_WIN_RESIZEABLE,1

dim waiting as BOOL

class FreeBASIC extends BASIC, QBASIC
....

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