[name_params] Flag arguments?
Dave, Daniel, I have a use case which would be nice to support. I have some functions which take some number of flag arguments, akin to: void foo(const char * name, float value, bool flag1 = false, bool flag2 = false) { std::cout << name << " = " << value << "\n"; } And I can add the named arg interface, so I can use it as: foo((value = 5.2f, name = "baz", flag1 = true)); But ideally I'd like the use to look like: foo((value = 5.2f, name = "baz", flag1)); That is, the presence of the keyword is enough to set the argument to true. Possible? -- -- Grafik - Don't Assume Anything -- Redshift Software, Inc. - http://redshift-software.com -- rrivera/acm.org - grafik/redshift-software.com - 102708583/icq
Rene Rivera wrote:
Dave, Daniel,
I have a use case which would be nice to support. I have some functions which take some number of flag arguments, akin to:
void foo(const char * name, float value, bool flag1 = false, bool flag2 = false) { std::cout << name << " = " << value << "\n"; }
And I can add the named arg interface, so I can use it as:
foo((value = 5.2f, name = "baz", flag1 = true));
But ideally I'd like the use to look like:
foo((value = 5.2f, name = "baz", flag1));
That is, the presence of the keyword is enough to set the argument to true. Possible?
Not with the current library, but it could very easily be added. Perhaps something like: bool flag1_ = args[flag1.implicit(true) | false]; What do you think? Dave? We could also just have all keywords have an implicit value true, but I think that might cause some problems for users. -- Daniel Wallin
Daniel Wallin <dalwan01@student.umu.se> writes:
Rene Rivera wrote:
Dave, Daniel, I have a use case which would be nice to support. I have some functions which take some number of flag arguments, akin to: void foo(const char * name, float value, bool flag1 = false, bool flag2 = false) { std::cout << name << " = " << value << "\n"; } And I can add the named arg interface, so I can use it as: foo((value = 5.2f, name = "baz", flag1 = true)); But ideally I'd like the use to look like: foo((value = 5.2f, name = "baz", flag1)); That is, the presence of the keyword is enough to set the argument to true. Possible?
Not with the current library, but it could very easily be added. Perhaps something like:
bool flag1_ = args[flag1.implicit(true) | false];
What do you think? Dave?
I like it. Implicit flags are optional by definition, right? Should bool flag1_ = args[flag1.implicit(true)]; be an error? And since bools will be by far the preferred flag type, should we just allow bool flag1_ = args[flag1.implicit]; ?? And should flag-ness be part of the keywords type struct foo_keywords : boost::keywords< boost::flag< flag1_t , is_convertible<mpl::_, bool> // #0 > , value_t > {}; So that we can accept foo(flag1) foo(value = 3) and reject foo(value) // #1 foo(flag1 = true) // #2 with SFINAE ?? Perhaps it is sufficient to reject #1 after overload resolution and make #2 legal. And should #0 be optional (since that would be the right default?)
We could also just have all keywords have an implicit value true, but I think that might cause some problems for users.
Yeah, it might. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com
participants (3)
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Daniel Wallin -
David Abrahams -
Rene Rivera