id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
1123	[program_options] patch - optional argument support (gnu getopt_long style)	anonymous	Vladimir Prus	"Attached is a patch to program_options that implements optional argument 
support, in the style of GNU getopt_long.  It adds one new method to 
'value_type': 'implicit_value()'.
The idea is that, if the option is given without an argument, it is assigned 
an ""implicit"" value.  Otherwise, if the long-option is given an explicit 
argument via the equals sign (--arg=value), or the short-option is given an 
adjacent argument (-avalue), the explicit value will override the implicit one.

For example:
desc.add_options()
 (""proxy,p"", value<int>(&proxy_port)->implicit_value(DefaultProxyPort), ""run 
proxy service"")
 ;
...
if (vm.count(""proxy""))
    enable_the_proxy(proxy_port);

./prog --proxy --opt2 --opt3
  -> enables proxy on default port.
./prog --proxy=9000 --opt2 --opt3
  -> enables proxy on port 9000.
./prog --opt2 --opt3
  -> does not enable the proxy.

"	Bugs	closed	To Be Determined	program_options	Boost 1.34.1	Not Applicable	duplicate