ProcedureReturn returning more than one value

[charvista]

Returning more than one value can be very handy.
I saw in another programming language this code:

Code: Select all

  def Geo::dec2dms(dec)
    s = dec * 3600
    d = (s / 3600).floor
    s -= d * 3600
    m = (s / 60).floor
    s -= m * 60
    return d, m, s
  end

Can this be implemented in PureBasic too?
Thanks for thinking about that...

[c4s]

I know this could be annoying but try using an structure for that.

[TomS]

I know this could be annoying but try using an structure for that.

How?

Code: Select all

Structure myStruct
	minutes.i
	hours.i
EndStructure  

Procedure bla(a,b)
	Protected time.myStruct
	time\hours = a
	time\minutes = b
	ProcedureReturn time
EndProcedure

Debug bla\minutes ; Error in this line

=> The variable has a structure

Code: Select all

Structure myStruct
	minutes.i
	hours.i
EndStructure  

Procedure.myStruct bla(a,b) ; Error in this line
	Protected time.myStruct
	time\hours = a
	time\minutes = b
	ProcedureReturn time
EndProcedure

Debug bla\minutes 

=> A structure can't be used with ProcedureReturn

[Fred]

Try this (not tested):

Code: Select all

Structure myStruct
   minutes.i
   hours.i
EndStructure 

Procedure bla(a,b, *result.myStruct)
   *result\hours = a
   *result\minutes = b
EndProcedure

bla(10, 20, @minutes.myStruct)
Debug minutes\hours
Debug minutes\minutes

[TomS]

Thank you.
I know this method and similar ones, but it's just not like PB. It looks more like C++
But it's an OK workaround, I guess.

[blueznl]

Fred, as you're reading this topic anyway ...

Would there ever be a change of procedures returning structures, or procedures returning multiple variables? It would be a great enhancement to the language, and clearly distinguish it from its lesser brethern

[Little John]

I just want to mention that it's also possible for a procedure, to return a pointer to a static structure inside the procedure. Here is a modification of Fred's example:

Code: Select all

Structure myStruct
   hours.i
   minutes.i
EndStructure

Procedure bla (a, b)
   Static result.myStruct
   
   result\hours = a
   result\minutes = b
   ProcedureReturn @result
EndProcedure

Define *time.MyStruct

*time = bla(10, 20)
Debug *time\hours
Debug *time\minutes

Regards, Little John

[TomS]

It has to be static. I don't know why, but otherwise I get a very high number (unknowing me guesses it is the pointer address?) and 0 as debugger-ouput.
But since a pointer to the static content is returned, every call of the procedure overrides everything, and every pointer is the same after all.

Code: Select all

Structure myStruct
   hours.i
   minutes.i
EndStructure

Procedure bla (a, b)
   Static result.myStruct
   
   result\hours = a
   result\minutes = b
   ProcedureReturn @result
EndProcedure

Define *time.MyStruct

*time = bla(10, 20)
*blub = bla(13,30)
Debug *time\hours ;With normal returns this would still be 10, but it is 13 now.
Debug *time\minutes

[Little John]

It has to be static.

Yes, I did write that. (Global or Shared would work as well.)
A local variable in a procedure does not exist anymore after the procedure has finished.

Regards, Little John

[charvista]

We can also do it by adding the needed pointers-variables as parameters:

Code: Select all

Procedure.d zDec2Dms(Dec.d,*D.integer,*M.integer,*S.integer)
    Seconds.d=Dec*3600
    Degrees.d=Int(Seconds/3600)
    Seconds-Degrees*3600
    Minutes.i=Int(Seconds/60)
    Seconds-Minutes*60
    *D\i=Int(Degrees)
    *M\i=Int(Minutes)
    *S\i=Int(Seconds)
EndProcedure

However, my wish here is just about returning more than one variable from a simple procedure without complications like pointers, structures,....
so I could export D, M, S easily.
I see that Blueznl is seconding this wish. (thanks!)

[TomS]

A local variable in a procedure does not exist anymore after the procedure has finished.

Thus the feature request for structured returns

I was aware of that method, too, but I dumped it, since it is only useful for one-time-calls like InitMyFramework().
Though Init-Functions mostly (always?) return only True or False or maybe ID or False^^

[DarkDragon]

It has to be static.

Yes, I did write that. (Global or Shared would work as well.)

But you should also mention that this is not threadsafe. For threadsafety you can use this:

Code: Select all

Structure TheStructure
  a.i
  b.i
  c.i
EndStructure

Procedure.i ThreadSafeMultiReturn()
  Protected *Result.TheStructure
  
  *Result = AllocateMemory(SizeOf(TheStructure))
  If *Result
    *Result\a = 10
    *Result\b = 20
    *Result\c = 30
    ProcedureReturn *Result
  EndIf
  
  Debug "Not enough memory?"
  ProcedureReturn #Null
EndProcedure

*Result.TheStructure = ThreadSafeMultiReturn()

If *Result <> #Null
  Debug *Result\a
  Debug *Result\b
  Debug *Result\c
  FreeMemory(*Result)
EndIf

[EDIT]
Or use the new Threaded keyword.

[TomS]

Ok.
Some people want this feature in everyday coding, which is fine. I'd like that too.
Others want to offer includes with commands that 'feel' like native PB-Commands.

If somebody is looking for that, here is what I do.
I use a global array for my objects.

Code: Select all

Structure Object
	size.i
	state.i
EndStructure

Global Dim id.Object(1)

Procedure CreateObject(size.i, state.i)
	Protected count.i = ArraySize(id())-1
	
	id(count)\size = size
	id(count)\state = state
	
	ReDim id(ArraySize(id())+1)
	
	ProcedureReturn count	
EndProcedure

Procedure SetObjectState(state.i, id.i)	
	id(id)\state = state		
EndProcedure 

Procedure GetObjectState(id.i)	
	ProcedureReturn id(id)\state	
EndProcedure

c = CreateObject(1, 2)
d = CreateObject(1, 4)
SetObjectState(78, d)

Debug GetObjectState(c)
Debug GetObjectState(d)
End

[DarkDragon]

An example with "Threaded" keyword for threadsafety:

Code: Select all

Structure TheStructure
  a.i
  b.i
  c.i
EndStructure

Threaded Result.TheStructure

Procedure.i ThreadSafeMultiReturn()
  Result\a = 10
  Result\b = 20
  Result\c = 30
  ProcedureReturn @Result
EndProcedure

*Result.TheStructure = ThreadSafeMultiReturn()

If *Result
  Debug Result\a
  Debug Result\b
  Debug Result\c
Else
  Debug "Failed?"
EndIf

But notice that you can't call ThreadSafeMultiReturn a second time inside the same Thread without loosing the old result and its just leading to bugs if you return the pointer as you might not remember the first part of my sentence.

[jamirokwai]

Returning more than one value can be very handy.
I saw in another programming language this code:

Code: Select all

  def Geo::dec2dms(dec)
    s = dec * 3600
    d = (s / 3600).floor
    s -= d * 3600
    m = (s / 60).floor
    s -= m * 60
    return d, m, s
  end

Can this be implemented in PureBasic too?
Thanks for thinking about that...

Would be great to have a ProcedureReturn with multiple values

I encountered a problem, where I like to have a String and two Integers given back from a function.
My approach was to use String + "|" + Str(i1) + "|" + Str(i2) and to use StringField to get back the info.
But you couldn't use this when your need Full Speed... :-O

Maybe like this!? Would be a great enhancement!!!

Procedure xyz(a,b,c)
return a,b,c
EndProcedure

(x,y,z) = xyz(a,b,c)