Reece Dunn wrote:
std::cout << io::object ( std::make_pair( 'a', 5 ), "{ " + fmt::pair()/" == " + " }" ) << '\n'; // output: { a == 5 }
Great. I wonder what others think? Personally, I really like the / operator. Probably that's because I've borrowed the idea from one parser generator which allows to write:
(literal / "," )
to mean a list of literals separated by ",".
Sure. Another alternative would be:
fmt::pair()[ " = " ]
but this may be confusing WRT the standard behaviour of the [] operator.
Yes, a bit confusing.
The opening and closing braces look less clear for me now. Maybe, we can use
fmt::pair("{", "}")/" == "
The problem with this is deducing that the parameters passed to fmt::pair or others are format objects (for formatting first and second data members) or delimiter strings or other arguments (e.g. DelimiterType or array length). This could possibly be done using MPL, but would further complicate the implementation.
I agree, this would cause too much difficulties.
fmt::braces("{", "}") + fmt::pair()/" == "
But I'm really really not sure.
Suggestions are always welcome.
fmt::braces is openclose_formatter in the review implementation (wrapper_decorators in the version I am currently working on). The problem with defining operator + for <open_close> + <open_close_separator> value holders is: how do you inherit values, for example:
fmt::braces( "<< ", " >>" ) + fmt::pair( "{ ", " }" )/" == "
is this: << a == b >> or: { a == b }
We need to see the full expression ;-) If that's cout << io::object(v, fmt::braces( "<< ", " >>" ) + fmt::pair( "{ ", " }" )/" == ") then clearly "{ a == b }".
This would be "<< a == b >>" in this instance, because fmt::pair will set the values and fmt::brace will cause them to be overrided.
Why? You can defined operator+ any way you like, and the second operand can override values from the first.
This is similar to this situation:
"<< " + fmt::pair().decorate( "{ ", " }" )/" == " + " >>"
This case is harder. The only reasonable behaviour is "<< a == b >>". But then, why would anyone write this? And if you use some formatter object, writing "<< + my_fmt + ">>" would have the reasonable effect of overriding separators. I recalled one more thing. In docs, you talk about FormatObject template parameter. But there is a class named "openclose_formatter_t". Note "formatter", not format_object. At one moment, I started to wonder what's the difference between "format object" and "formatter". I suggest that you use only one term everywhere. And also, template parameter for arrayfmt_t is called FormatObject. I think it would be clearer to call it "NestedFormatObject" or "NestedFormatter". - Volodya