Dim Byref syntax

[dkl]

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]

I prefer the syntax with which you started!

[stylin]

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

[VANYA]

With Byref better.

[grindstone]

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]

interesting concept!

i think i'd prefer "dim as byref integer"

[fxm]

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

[grindstone]

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]

@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]

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

[grindstone]

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]

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]

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)

[fxm]

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

[D.J.Peters]

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
....