David Abrahams wrote:

"Reece Dunn" <msclrhd@hotmail.com> writes:

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I'm generally not a great fan of statefulness, but this also seems like a reasonable thing to want:

namespace io = boost::io; std::cout << io::sequence_delimiters("{ ", " }"); std::cout << io::sequence( vec ); // output: { 1, 2, 3 }

You can achieve something like this using:

io::formatter< const char * > fmt( "{ ", " }" ); std::cout << io::sequence( vec ).format( fmt );

If there are any better alternatives, I am willing to listen.

Well, I think my alternative is better if you want a stateful change, since yours doesn't accomplish that. My suggestion is certainly consistent with normal io manipulators. The point is to stream a bunch of sequences without having to repeat the format part.

I understand what you are saying and yes your version is neater. However, implementing something like this would have performance penalties (because you will need to create/store the preset values at run-time). It will also change the way all sequence constructs are rendered. (n-ary types have a different rendreing so won't be affected). As I understand, this is the desired effect. But then: [1] how do you select sequence or n-ary formatting? [2] what about extending this to incorporate - for example - tree or string formatting? [3] how do you extend this to formatter types that have additional delimeters? [4] how do you know when to extract the default delimeter values from the stream? Adding a formatter as a parameter to io::sequence, etc. would further complicate function lookup. Perhapse if I had an is_format_object< T

::value trait I could use MPL wizardry to distinguish between format object and delimeter formatter, allowing:

io::formatter< const char * > fmt( "{ ", " }" ); std::cout << io::sequence( vec, fmt ); // output: { a, b, c } The problem with this is: what if you want to specify a format object and a delimeter formatter? This might work, but the implementation becomes more complex. Another idea would be to overload an operator like: std::cout << io::sequence( vec )( fmt ); // output: { a, b, c } or std::cout << io::sequence( vec )[ fmt ]; // output: { a, b, c } but this would further add to the confusion. If operator() was adopted, it would be possible to have that as a shorthand for format(). For example: std::cout << io::sequence( vec )( " | " ); // output: [ 1 | 2 | 3 ] Regards, Reece _________________________________________________________________ Express yourself with cool new emoticons http://www.msn.co.uk/specials/myemo