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Subject: [boost] [convert] Default Syntax Idea
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-02-24 14:52:53

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.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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