Hi,
I'm having a bit of a discussion with some colleagues about assignments.
I'm trying to come up with a example (or two) in which the use of an
assignment expression as an RValue is the only (best?) way to do it.

  eg..
   someOperation(X = SomeExpression);

So far, it seems that one can always do ...

   X = SomeExpression;
   someOperation(X);

and a half decent optimizer will generate the same code.

Even ...

   A = B = C = D;

can be expressed as ...

   C = D;
   B = D;
   A = D;

So can anyone help me with an example, or is such a beastie just a syntax shorthand?


-- 
Derek
Melbourne, Australia
10/Aug/04 1:57:47 PM

Derek Parnell wrote:
> Hi,
> I'm having a bit of a discussion with some colleagues about assignments.
> I'm trying to come up with a example (or two) in which the use of an
> assignment expression as an RValue is the only (best?) way to do it.
> 
>   eg..
>    someOperation(X = SomeExpression);
> 
> So far, it seems that one can always do ...
> 
>    X = SomeExpression;
>    someOperation(X);
> 
> and a half decent optimizer will generate the same code.
> 
> Even ... 
> 
>    A = B = C = D;
> 
> can be expressed as ...
> 
>    C = D;
>    B = D;
>    A = D;
> 
> So can anyone help me with an example, or is such a beastie just a syntax
> shorthand?

I prefer for local variables to exist only where they are used, so it's useful to be able to write something like this:

    if (DerivedClass* derivedPtr = dynamic_cast<DerivedClass>(some_base)) {
        ...
    }

The local 'derivedPtr' exists only within the if block, where it belongs.

The only other way to do this is to create a naked block just for the if statement.  It works, but it's much uglier looking and involves another level of nesting. (opinions may vary)

 -- andy