[boost] [range] adaptors vs. rvalue to lvalue& binding

22 Mar 2012

      Hello,

ideally I would like to use range-adapted lvalue ranges like any other lvalue ranges. Writing it down naively, as below, does not compile because LoadRefRange takes (and should take?) the range it modifies by lvalue&, while adaptor expressions are rvalues.

template<typename Range>
void modifies_range( Range& rng );

A a[5];

main() {
      // modifies all elements of a
	modifies_range ( a );

      // modifies all elements (except for one) of a
	// adaptor is rvalue, does not compile:
      modifies_range (
		boost::range::join(
			boost::adaptors::slice( a, 0, 1 ),
			boost::adaptors::slice( a, 2, countof(a) )
		)
      );

	// compiles, but ugly:
	auto rng=boost::range::join(
		boost::adaptors::slice( a, 0, 1 ),
		boost::adaptors::slice( a, 2, countof(a) )
	);
	modifies_range(rng);
}

Any thoughts? Should adaptors receiving lvalues offer an 

	operator adaptor&() &&; // overload on rvalue-ness

so they are passing through the lvalue or their argument? A suitable baseclass a la boost::additive could do that.

Regards,

Arno

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