Daniel Wallin <dalwan01@student.umu.se> writes:
Joel de Guzman wrote:
1) WRT DSL, I'm not quite sure about the syntax for defaults. Example: params[name | "unnamed"] I have a strong feeling that there's a better syntax but I am not sure what it is now. I read in the thread that the syntax params[name] | "unnamed" is not doable, but I'm not quite sure. Perhaps a clarification will set me straight. Having the default in the brackets seems to rather awkward. Perhaps: params[name].defaults_to("unnamed") is better?
That has exactly the same problem as having the | outside the brackets. The problem is that operator[] would need to return something other than the actual parameter reference, something that:
1) Is convertible to the parameter type.
We still need params[name], with no default to work.
2) Has operator|() or defaults_to() member function.
So, we'd need a conversion operator. But if we have a conversion operator, we can't reliably pass the arguments to function templates because the type deduction will go wrong.
One possible alternative is params.defaults_to("unnamed")[name] but I find that highly illogical to read, because the specification of the default precedes the keyword it's defaulting. However, Thorsten's prodding has made me wonder if we need || for the lazy case at all. It seems as though params.has(name) ? params[name] : something_else; is superior in every way except brevity. And there will be substantial cases where it's briefer as well, because there's no need to build a function object for something_else. Am I missing something? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com