Re: reference to non-const temporary

From:

fgothamNO@SPAM.com (Frederick Gotham)

Newsgroups:

comp.std.c++

Date:

Thu, 27 Jul 2006 14:56:18 GMT

Message-ID:

<Ji2yg.11914$j7.320327@news.indigo.ie>

Ethan Eade posted:

I'm curious -- why aren't temporaries allowed to be passed as non-const
references?

If you pass either:

(1) non-const reference
(2) pointer to non-const

to a function, then that implies that the function is going to alter
something.

Logic dictates that you only alter something if there's a reason to.

If you pass a temporary, then any such alterations will be lost.

It seems slightly arbitrary, since non-const methods can be
called on them anyway.

But it still ensures that we don't discard alterations.

Surely such temporaries are fully constructed
objects. What's the rationale? It seems the restriction is trivially
circumvented using operator=():

struct Foo {};

Foo make() { return Foo(); }

void use(Foo& foo) { }

int main()
{
use(make()); // Fails, as discussed above
use(Foo() = make()); // Compiles
}

This I just plain don't understand. In the last line in "main", it appears
you're assigning to an R-value.

Since when can we assign to an R-value?

Furthermore, since when can this R-value then be passed by non-const
reference... ?

--

Frederick Gotham

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