Re: [boost] Re: class proposal

From: Justin M. Lewis (boost_at_[hidden])
Date: 2003-04-23 20:14:01

Yes, it is better.

The first example has the problem of, you still have to go look up the
function to see if it's actually changing anything, or if it's taking the
param in, reading teh value, then modifying based on what was read.

The second example has the problem of copying a potentially large object,
and it doesn't allow for in/out params.

----- Original Message -----
From: "Gregory Colvin" <gregory.colvin_at_[hidden]>
To: "Boost mailing list" <boost_at_[hidden]>
Sent: Wednesday, April 23, 2003 5:34 PM
Subject: Re: [boost] Re: class proposal

> On Wednesday, Apr 23, 2003, at 16:07 America/Denver, Justin M. Lewis
> wrote:
> > Sorry if the explanation is a bit confusing.  The whole idea here is to
> > make it explicit at the function invocation that a parameter being
> > passed will be used to return a value.
> >
> > A good example of where this would be useful is with a function call
> > that takes some params, and returns several different things in
> > different params, and still has an explicit return for an error code.
> > At the invocation point it would be impossible to tell what's going on.
> >
> > int chk;
> > chk = GetSomething(p1, p2, p3, p4, p5);
> >
> > where the actual declaration of GetSomething is like
> >
> > int GetSomething(int &ret1, int &ret2, int v1, int v2, int v3);
> >
> > It's impossible to tell at the invocation which params are returning,
> > and which are being used to calculate the return.  At the invocation it
> > looks like chk might be what you're trying to get.
> >
> > With classes like I'm suggesting it would be obvious, the declaration
> > would be:
> > int GetSomething(c_out<int> ret1, c_out<int> &ret2, int v1, int v2, int
> > v3);
> >
> > And at the invocation now, it has to be explicit that those first 2
> > params are out params.
> >
> > chk = GetSomething(out(p1), out(p2), p3, p4, p5);
> >
> > It REQUIRES you to use the out helper function at the invocation, so
> > anyone reading the code later can see, without checking the
> > implementation of GetSomething, that those 2 params are being set, and
> > the last ones are not.
>
> Is this really that much better than
>
>     chk = GetSomething(&p1, &p2, p3, p4, p5);
>
> or
>
>     GotSomething ret = GetSomething(p3,p4,p5);
>
> ?
>
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