🚀 go-pugleaf

In article <47l76s$qu1@watnews2.watson.ibm.com>, jjb@watson.ibm.com (John Barton) writes:
|> In article <47dn87$a17@sunsystem5.informatik.tu-muenchen.de>,
|> schuenem@informatik.tu-muenchen.de (Ulf Schuenemann) writes:
|> |> In article <46vaga$dng@marina.cinenet.net>, scotty@cinenet.net (J Scott
|> |> Peter XXXIII I/III) writes:
|> |> |> a += b	=>  a = a + b
|> |> |> a + b	=>  tmp = a; a + b; tmp
|> |> |> Similarly for other composite operators.
|> |> |>
|> |> |> a != b	=> !(a == b)	and vice versa
|> |> |> a >= b	=> !(a < b)	etc
|> |> |> a < b	=> a - b < 0	etc
|> |> |> a - b	=> a + (-b)	and vice versa
|> |> |> -b		=> 0 - b
|> |> |> +b		=> b
|> |> |> a++		=> a += 1	also --
|> |> |> a->b		=>  (*a).b
|> |>
|> |> The standard header <utility> (20.2.1) already defines template-
|> |> operators for the relational operators, deducing them to == and <
|> |> a != b		=> !(a == b)
|> |> a >  b		=>   b < a
|> |> a <= b		=> !(b < a)
|> |> a >= b		=> !(a < b)
|> |>
|> |> You can extend this idea:
|> |>
|> |> template<class T> T& operator+=(T&a, T&b) { return a = a + b; }
|> |> template<class T> T  operator- (T&a, T&b) { return a + (-b); }
|> |> template<class T> T  operator- (T&a)      { return 0 - a; }
|> |> template<class T> T& operator+ (T&a)      { return a; }
|> |> template<class T> T& operator++(T&a)      { return a += 1; }
|> |> template<class T> T& operator++(T&a,int)  { return ++a; }
|> 
|> This will not work: it prevent you from writing any templates
|> for these operators over types that do not have "1" or "0"
|> or that need a definition other than the one above.
|> 
|> --
|> John.
|> 
|> John J. Barton        jjb@watson.ibm.com            (914)784-6645
|> 	<http://www.research.ibm.com/xw-SoftwareTechnology>
|> H1-C13 IBM Watson Research Center P.O. Box 704 Hawthorne NY 10598
|> ---
|> [ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
|>   Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
|>   is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]

The substitution for a+=b also won't work; if evaluation of a
has a side effect the side effect will happen twice.  

--
rp

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