Opened 10 years ago
Closed 6 years ago
#7495 closed Feature Requests (fixed)
Support for boost::optional in boost::program_options
| Reported by: | Owned by: | Vladimir Prus | |
|---|---|---|---|
| Milestone: | To Be Determined | Component: | program_options |
| Version: | Boost 1.52.0 | Severity: | Optimization |
| Keywords: | Cc: |
Description
It would be nice to allow support for boost::optional<T> arguments in program_options, so you can write following:
optional<std::string> optionalArg; options_description desc("allowed options"); desc.add_options() ("optional", value(&optionalArg), "specify optional argument");
And shouldn't bother with argument checking using variables_map.
Change History (8)
comment:1 by , 8 years ago
comment:3 by , 7 years ago
you only need to include this piece of code
template<class T> std::istream& operator>>(std::istream& in, boost::optional<T>& obj) {
T value; in >> value; obj = value; return in;
}
comment:4 by , 7 years ago
It would seem such streaming support should be done in the optional library, not in program_options?
comment:5 by , 7 years ago
Implementing optional support via streaming would have unwanted side effects. The correct place to implement optional support is via the validate customization point:
namespace boost {
template<class T>
void validate(boost::any& v, std::vector<std::string> const& values, boost::optional<T>* typeTag, int)
{
if (!values.empty())
{
boost::any a;
using namespace boost::program_options;
validate(a, values, (T*)0, 0);
v = boost::any(boost::optional<T>(boost::any_cast<T>(a)));
}
}
}
comment:6 by , 7 years ago
Pull request will be welcome. Is there a way to implement this with a forward declaration, so that program_options do not have to depend on boost::optional.
comment:7 by , 7 years ago
Submitted pull request: https://github.com/boostorg/program_options/pull/18
Uses forward declaration to avoid dependency (except in tests).
comment:8 by , 6 years ago
| Resolution: | → fixed |
|---|---|
| Status: | new → closed |
I am very interested in this as well!