I'm not exactly sure I understand.  I've always understood that FB can pass
by value or address.

FN callByValue(thisValue,thatValue)
FN callbyAddress(@thisValue,@thatValue)


In FB either the caller or the called function can determine how variables
are passed.

local fn receiveByValue(incomVal1,incomVal2)
end fn

local fn receiveByAddress(@incomVal1,@incomVal2)
end fn

unless the caller is already passing by address I think its pretty clear the
passing method.

Is larry suggesting a way to force a ram variable in the callees paramater
list?

I may have missed some critical point but I dont think so.


W.


-----Original Message-----
From: Robert Purves [mailto:robert.purves@...]
Sent: Tuesday, April 24, 2001 1:34 AM
To: futurebasic@...
Subject: Re: [FB] Re: ~Vars as parameters



>I was proposing that ~ serve to designate a FN variable to be a
>Pascal Var. There are a few VARs in FB already.  For example,
>INC(X%) changes X%,  so X% is a VAR in INC().

> > Before we get into it, I need a clear example of what
> > you are doing that can't be accomplished under the
> > current structures. I am missing the boat somewhere.
>
>Yes, the issue is *not at all* what can be done but rather how
>fast and smoothly and simply things can be done.


A parameter can be passed to a FN or function or procedure _either_ by
value (the only method supported by FB), _or_ by address (the only method
that was supported by QB). In the latter case only, changes in the
parameter get transmitted back to the caller.
Pascal and C allow parameters to be specified in either way.

The usefulness of Pass-By-Address is evident in tbis quandary:

// How can I return two values from this FN?
local fn SumAndDiff( a#, b# )
dim sum#, diff#
sum  = a + b
diff = a - b
end fn


Larry's proposal would allow an elegant solution:

local fn SumAndDiff( a#, b#,  ~sum#, ~diff# )
sum  = a + b
diff = a - b
end fn

dim @ s#, d# // must be RAM variables for Pass-By-Address
fn SumAndDiff( 4.0, 3.0, ~s, ~d )

print s, d  '<--- would print   7     1


Robert P.



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