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Date: Tue, 18 Jun 2002 11:45:17 -0400
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: status of Ada STL?
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Date: 2002-06-18T11:45:17-04:00
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Fraser Wilson wrote:
> C++ seems to tie itself in knots over the issue of temporaries, which
> is why constructs such as the above have to be used.

The arithmetic assignment operators all existed in C, some decades
before C++ ever existed. The usual argument is that when you are
operating on a long name, you don't want to say it more than once -

	myArray[10].subfield1.subarray[5].z /= 2;

More likely, it helps with stepping through an array with a
post-incrementing pointer, where you simply cannot repeat the
name of the object -

	while (begin != end) *begin++ /= 2;

As far as temporaries go, it's simply a fact that operating
in place on an object is likely to be more efficient than
making a new one and copying it about. For reasonably complex
objects, it is hopeless to think that the compiler can raeson
this out for you. The usual C++ technique is to write the
infix operators in terms of the assignment ones -

	struct X
	{
		X &operator/=(const X &other)
		{
			/* do something */
			return *this;
		}
		X operator/(const X &other)
		{
			X x = *this;
			return x /= other;
		}
	};