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From: pkturner@cup.portal.com (Prescott K Turner)
Newsgroups: comp.lang.c++
Subject: Re: Use of temporaries in assignments
Message-ID: <30152@cup.portal.com>
Date: 23 May 90 04:41:01 GMT
References: <2654126F.17958@paris.ics.uci.edu>
Organization: The Portal System (TM)
Lines: 32

rfg@paris.ics.uci.edu (Ronald Guilmette) writes:
> // I have just started to look at the code generated for simple statements of
> // the general form:   base = derived;
> //
> // It seems that the legality of such statements relies on the use of
> // base::operator=(const base&) operators (which are implicitly generated
> // by the compiler when not explicitly declared) and upon automatic implicit
> // (multi-stage?) conversions of values of type `derived' to values of type
> // `base&'.
More precisely, an lvalue of type derived is converted directly to a reference
to base.

> // It seems to me that uses of these (sometimes implicitly generated) assignm
ent
> // operators should mean that statements of the general form shown above shou

> // never involve the creation of temporaries or calls to constructors or
> // destructors.
The rule for initializing references changed as of cfront 2.0.  It applies
to parameters such as the "const base &" in the implicitly-generated
assignment operator for base.  For certain types of actual arguments,
a temporary is created (implying calls to constructors and destructors).

>   base_object = derived_object;
In this assignment statement, the derived object is not const.  I don't think
the annotated reference manual is clear on this, but it seems sufficient
grounds for cfront to create a temporary.
--
Prescott K. Turner, Jr.
Language Processors, Inc.
959 Concord St., Framingham, MA 01701 USA    (508) 626-0006 x232
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