Digest for comp.lang.c++@googlegroups.com - 3 updates in 2 topics

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• Multi-compare operators - 1 Update
• Variadic template and arguments by value - 2 Updates

Multi-compare operators

Bart <bc@freeuk.com>: Sep 24 11:15PM +0100 On 24/09/2018 21:53, Vir Campestris wrote: >> number of precedences.   > ... which is why I bracket everything. I'm "agnostic" in this - I don't > know the full order of precedences, and I don't believe you do either.   Tim Rentsch does. I think he expects everyone else to as well (as you might notice in his code).   -- bart

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Variadic template and arguments by value

ram@zedat.fu-berlin.de (Stefan Ram): Sep 24 09:22PM > }; >Both look like an "universal reference" situation, but apparently >the second isn't?   Yes, because the second template does not directly precede the function.   And then, I believe, the following might happen here:   When you call   instantiate( a, b, c )   ,   Types...   in »instantiate« is deduced to be »( int&, int&, int& )«, so the return type of »instantiate« is   MyClass< int&, int&, int& >   , thus the constructor now has the (hypothetical) signature   MyClass( int & &&, int & &&, int & && ) {}   and, IIRC, this is reduced to   MyClass( int &, int &, int & ) {}   . So you might be using a constructor with lvalue reference parameters, in which case it would be no surprise that it accepts lvalue arguments!   Disclaimer: I'm not actually familiar with these techniques, so I might be totally wrong!

ram@zedat.fu-berlin.de (Stefan Ram): Sep 24 09:52PM >in »instantiate« is deduced to be »( int&, int&, int& )«,   No parameter packs are required to see this. The following example suffices.   template< typename T >void c( T && ){} template< typename F >void f( F && r ){ c< F >( r ); } int main(){ int a = 1; f( a ); }   When »f( a )« is called, »F« becomes »int&«, and c accepts lvalues. When »f( 1 )« is called, »F« becomes »int«, and c accepts rvalues.

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