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Subject: Re: [boost] [explore] Library Proposal: Container Streaming
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2009-12-01 12:22:38

> Michael Caisse wrote:
> > I've been trying to think of when I might use such a library. Without
> > the symmetry (input as well as output) I can think of few instances
> > where this functionality might come in handy. Other than potential
> > debug output, what else do you envision? What am I missing?
> Yes, I mostly think of this for debug output. But that does come up
> a lot. Similar to debug output would be testcase output. Something
> the customer still does not see, but is certainly useful. An example
> of something in production code might be printing a container out as
> an html table.

What about:

    os <<
            "<ol>" <<
                *verbatim["<li>" << stream << "</li>"]
            << "</ol>", // format description
            '\n', // delimiter
            c // data
        ) << std::endl;

(ok, not a table, but a list, but you get the idea) where c could be any
container type holding any data type.
And with some preparation it is easily possible to create a special html
framework allowing to write this as:

    html::ol[*html::li[stream]] or

> > I'm also finding little improvement over the following example
> > based on your samples. Here I am using Karma to produce the same
> > output as Explore. It is a bit more verbose; however, it is
> infinitely
> > more flexible.
> In BoostCon 2007, we wanted something that worked like 'print(c)' where
> 'c' is any container. Other languages have this capability. We did
> consider using Karma during that conference and somebody presented
> this. It was decided to not be simple enough. The code samples you
> provided are compelling, but it's not as dead simple as 'print(c)' or
> the more C++ oriented 'cout << c'.

'cout << c' just doesn't work because of the need to use UB (extending
namespace std). So you will end up writing

    cout << explore::format(c);

which would have the Karma equivalent of (Boost V1.41):

    cout << karma::format(*stream, c);

or even (post V1.41):

    cout << karma::format(auto_, c); or
    cout << karma::format(c);

Regards Hartmut

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