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From: richard@ex-parrot.com (Richard Smith)
Newsgroups: comp.std.c++
Subject: Re: Idea for calling multiple methods on a single object.
Date: Mon, 7 Jun 2004 16:47:14 +0000 (UTC)
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bekkah@web.de (Helium) wrote in message news:<194c1211.0406060903.6731d4ee@posting.google.com>...
> Multiple method-call:
  [...]
> Another possible solution is to store the rusult somewhere.
> 
> {
>    Type tmp = foo ();
>    tmp.method1 ();
>    tmp.method2 ();
> }
> 
> 
> This is very unconvenient and the result has to be copied which cvan
> be time consuming as well.

So use a reference:

  Type const& tmp = foo();
  tmp.method1();
  tmp.method2();

> And you have to know the function's return
> type. 

This is true.  Hopefully the next version of the Standard will allow
this to be solved using the auto keyword:

  auto const& tmp = foo(); // Or whatever the syntax is going to be.
  tmp.method1();
  tmp.method2();

>If it's a reference to an object its type isn't know at
> compile-time, 

You mean the type needn't be complete: it is still known.

>so you have to use a reference, too. If it's a temporary
> object you can't store it in a reference but you have to make a copy
> of it. 

You can bind a temporary to a reference which extends the lifetime of
the temporary.  Suppose foo() returns a Type by value, I can still
write

  Type const& tmp = foo();

and the lifetime of the temporary is extended for the lifetime of the
reference. (The compiler is allowed to make a copy of the return
value, but a good compiler will not.  -- See 8.5.3/5, bullet 2,
sub-bullet 1.)

> In both cases you have to create an additional temporary
> (weither a reference or a complete object).

Creating a reference is very cheap.  It may well not involve any
additional runtime overhead.

--
Richard Smith

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