Re: [boost] [type_erasure] Review started (July 18-27, 2012)

Subject: Re: [boost] [type_erasure] Review started (July 18-27, 2012)
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2012-07-26 14:15:05

-----Original Message-----
From: boost-bounces_at_[hidden] [mailto:boost-bounces_at_[hidden]] On Behalf Of Lorenzo
Caminiti
Sent: Wednesday, July 18, 2012 6:13 AM
To: boost_at_[hidden]; boost-announce_at_[hidden]; boost-users_at_[hidden]
Subject: [boost] [type_erasure] Review started (July 18-27, 2012)

*** The review of Steven Watanabe's proposed Boost.TypeErasure library begins on July 18, 2012 and
ends on July 27, 2012. ***

I'll post a fuller review in due course, but after playing with this I am tempted to cut to the
chase and say YES.

But here is an example that I have knocked up in a few minutes from print_sequence.cpp example
(after a longer time struggling with the name TypeErasure and the concept in the docs).  

#include <libs/units/example/measurement.hpp>  // An uncertain type called measure.

    int test[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    double testd[] = { 1., 2., 3., 4., 5., 6., 7., 8., 9., 10. };
    quantity<length> testq[] = {2345.6 * meters, 123.4 * meters, 0.0123 * meters};
    quantity<length, measurement<double> > testqu[] = {measurement<double>(45210.0, 1234.0) *
meters,   measurement<double>(789, 2.5) * meters, measurement<double>(0.000567,2.34e-5) * meters};

    separator_printer p1(",  "); // Construct a printer.
    p1.print(std::cout, test); // 1,2,3,4,5,6,7,8,9,10
    std::cout << std::endl;

    separator_printer p1a("___"); // Construct a printer with underscore separator.
    p1a.print(std::cout, test); // 1___2___3___4___5___6___7___8___9___10
    std::cout << std::endl;

    p1.print(std::cout, testd); // Type now double.
    std::cout << std::endl; // 1,2,3,4,5,6,7,8,9,10

    std::cout.precision(5); // Make some fancy layout.
    std::cout << std::showpos << std::showpoint << std::endl;

    p1.print(std::cout, testd); // Type still double.
    std::cout << std::endl; //
+1.0000,+2.0000,+3.0000,+4.0000,+5.0000,+6.0000,+7.0000,+8.0000,+9.0000,+10.000
    std::cout << std::noshowpos << std::endl; // Switch off fancy +.

    p1.print(std::cout, testq); // Type now quantity of length.
    std::cout << std::endl; // 2.3456 km,  123.40 m,  12.300 mm
    // Note the cool change of unit prefix from km to m to mm!

    p1.print(std::cout, testqu); // Type now quantity of length with uncertainty estimate.
    std::cout << std::endl; // 45.210(+/-1.2340) km,  789.00(+/-2.5000) m,  567.00(+/-23.400) um
    // Note the cool change of unit prefix *and* showing uncertainty!

I'm impressed !

Now if I can manage to string enough neurons together to write my own 'printers' etc, ...

But already I sense this is a must-have bit of software.

:-)

Paul

PS I can't come up with a better name than TypeErasure but it is certainly a bit forbidding :-(