formal parameter in GLOBAL list

[tsh73]

If formal parameter is in GLOBAL list
then
    factual parameter does not used then calling function - global variable gets called instead.

Here's (simplified) code that made me really puzzled today.
global n
n=10

call doSomeTests

input "press ENTER"; a$
end

sub doSomeTests
   nMax = 100
   print "Just print ";n;" random numbers from 0 to ";nMax-1
   for i = 1 to n
       print rand(nMax)    'nMax is not used
   next
end sub

function rand(n)    'now because n is global, global 'n' is used - it is a bug
   rand = int(rnd(0)*n)
end function


Expected output: numbers in range 0..99
Real output: numbers in range 0..9

[Brandon Parker]

In my opinion this isn't a bug.

Since Liberty BASIC doesn't have a Global/ Local descriptor for the function definition how would the compiler determine whether or not the code calling the function wants to use the variable being passed or the global variable.

One should not use Global variables inside functions and expect that variable to be considered Local by the function.

This is just my opinion, but I do not believe I would consider this a bug; it is how the language works.

{:0)

Brandon Parker

[Carl Gundel]

I think it's a bug.

[Rod]

Ah, I thought it wasn't a bug too but I see what Anatoly is saying now.

function rand(n) 'now because n is global, global 'n' is used - it is a bug
rand = int(rnd(0)*n)
end function

Its not that a global value is passed to the sub its that a global value is not updated when used as a receiver in the sub. In Anatoly's code above you would have expected the global variable n to be updated with the value passed as nMax

[Carl Gundel]

Aug 16, 2018 4:56:03 GMT -5 Rod said:

Ah, I thought it wasn't a bug too but I see what Anatoly is saying now.

function rand(n) 'now because n is global, global 'n' is used - it is a bug
rand = int(rnd(0)*n)
end function

Its not that a global value is passed to the sub its that a global value is not updated when used as a receiver in the sub. In Anatoly's code above you would have expected the global variable n to be updated with the value passed as nMax

If a variable is defined as a parameter into the function it cannot be treated as a global.  It must be its own local variable of the same name.

It's remarkable that this one has escaped our attention for a very long time.

[Rod]

Ugg, back to being confused. Global surely means global and so any named global is global. Say we had a convention of capitalising globals. I would not expect Max in the main program or Max in the sub or function to be a different variable. Currently Max is not updated as a receiver, fix that then everything falls into place for me.

[Carl Gundel]

Aug 16, 2018 11:10:55 GMT -5 Rod said:

Ugg, back to being confused. Global surely means global and so any named global is global. Say we had a convention of capitalising globals. I would not expect Max in the main program or Max in the sub or function to be a different variable. Currently Max is not updated as a receiver, fix that then everything falls into place for me.

If I specify a function which has an parameter name of x, that should override the global inside that function.  Otherwise how can my program use a function written by someone else if a local variable is accidentally hijacked by a global declaration?

The following should produce the number 12.  The print test(6) line passes in the value 6, and x should be 6 inside the scope of that function, not 5.

So, if we were to decide that it's okay for the global to behave the way it does, then at least some sort of compiler warning would be helpful.

global x
x = 5
print test(6)
end

function test(x)
  test = x*2
end function

[Rod]

Naw, global is global. You need a transcending global id, say "Max" then Max is Max no matter where it appears but if you assign it as a receiver in a sub it should take the passed value. Otherwise you don't pass it you simply use it or update it.


So I cannot see how you can assign a global "Max" and then expect subs and functions to ignore its global status.


So still very much confused. But that's getting more common as I age.

[Carl Gundel]

Aug 16, 2018 13:35:33 GMT -5 Rod said:

Naw, global is global. You need a transcending global id, say "Max" then Max is Max no matter where it appears but if you assign it as a receiver in a sub it should take the passed value. Otherwise you don't pass it you simply use it or update it.


So I cannot see how you can assign a global "Max" and then expect subs and functions to ignore its global status.


So still very much confused. But that's getting more common as I age.

That's why I wrote that if we decide it is not a bug, there should be a compiler warning so when it happens there is no confusion.

There's nothing earth shaking about this, because this has been going on a long time and LB is still usable.