Re: [boost] Re: Is output formatting like Spirit? Was: Re: Formal reviewof "Output Formatters" library begins today

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-09-23 16:20:33

Larry Evans wrote:
> On 09/23/2004 02:35 PM, Hartmut Kaiser wrote:
> [snip]
> 
>> My point wasn't the concrete syntax, this is volatile at this stage 
>> anyway.
>> My point was the concept to implement a library, which is 'dual' to 
>> Spirit,
>> based on the idea, that a grammar describes all possible matchable input
>> sequences, so why not use this 'grammar' to specify, how to generate this
>> input sequences.
> 
> Also, couldn't these 'dual' libraries be used to generate test cases
> for each other?

Sure. This would be good for performing a feature-by-feature comparison. 
Hooking the machinery into Boost.Test would be a good way of getting the 
results. Naturally, the test cases for each library should pass their 
own tests on supported platforms; the interesting cases will be the test 
cases from the other libraries.

How do we implement the tests? I suggest that we split the information into:

[1] the data type (type) being formatted, e.g. std::map< std::string, 
std::string > with the details of its contents;

[2] for output -- the string (str) such that:
    type val = ...;
    ostringstream ss;
    ss << some_fn( val );
    BOOST_TEST( ss.str() == str );

[3] for input, the string (str) such that:
    type val = ...;
    type read;
    istringstream ss( str );
    ss >> some_fn( read );
    BOOST_TEST( is_equal( read, val ));
where
    is_equal( const T & a, const T & b )
returns true iff a == b.

This would then provide a basis for comparison between the libraries, 
including: does the library support formatting of this form? and what 
are the differences in the code used to perform the formatting? For example:

    // review-style outfmt:
    ss << io::formatob( vec. io::containerfmt().format( "< ", " >" ));

    // new-style outfmt:
    ss << io::object( vec. fmt::container().decorate( "< ", " >" ));

    // Volodya-style outfmt:
    ss << io::object( vec, "< " + fmt::container() + " >" );

    // Torjo-style outfmt:
    // note: $ is used because it would be infrequently used as
    //    part of a decoration (escape = '\$')
    ss << io::object( vec, fmt::container()( "< $*$ >" ));

    // decoration-on-stream outfmt:
    ss << cdecorate( "< ", " >" )
       << io::object( vec, fmt::container());

    // type deduction in outfmt:
    ss << io::object( vec ).decorate( "< ", " >" );

Regards,
Reece