Re: [boost] [convert] Default Syntax Idea

Subject: Re: [boost] [convert] Default Syntax Idea
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2009-02-24 16:36:35

Stewart, Robert wrote:
> I was thinking a bit about syntax for the default value for the
> notional boost::convert() and kin.  How about the following:
> 
> int const i(3); string const s("something"); int const
> j(convert<int>(s) | 5);
> 
> convert<DestType,SourceType>(SourceType) can return a type which
> throws on failure in operator DestType(), but has an operator
> |(SourceType) which returns a second type constructed with the
> SourceType value.  The second type provides its own operator
> |(SourceType) which returns that value in its operator DestType() on
> failure.
> 
> Returning a default value in lieu of an exception is a special case;
> it ought not be treated like formatting.  Thus, while Boost.Parameter
> might be appropriate to package the extra information desired for
> formatting, I don't like the idea of writing "default_ = 5" in the
> call, and I don't think ", 5" in the argument list is as clear as it
> could be.  The syntax above is obvious and concise while being
> distinct from whatever may be done for formatting.

That's a nice idea. The default value may indeed be special enough to 
support this syntax.