Unexpected behavior with add_flag and std::optional<bool>

[sg-james]

Using a recent (2021-12-27) 9ec0ba7 build, under msvc14.1x64 (2017)

I want to represent a std::optional<bool> flag so I tried

std::optional<bool> opt_bool;
CLI::App app = ...
assert(opt_bool.has_value() == false); 
CLI::Option* opt = app.add_flag("--flag,!--no-flag", opt_bool, "My flag desc.");
assert(opt_bool.has_value() == false); // incorrectly (to me) is true

but opt_bool.has_value() is always true after add_flag(..)

I can work around this via

1. using opt->count() > 0 to reset the optional or

auto callback =  [&opt_bool](int value){
	if (value == 1) opt_bool = true;
	else if (value == 2) opt_bool = false;
};
CLI::Option* opt = app.add_flag("--flag{1},--no-flag{2}", callback, "My flag desc.");

but was wondering if the first approach was meant to work as I had hoped?

Here's a simple project that demonstrates it: https://godbolt.org/z/cxzaY3o3s

[phlptp]

let me take a look, not sure I have tried anything with an optional bool

[phlptp]

I did verify the behavior you were seeing, has to do with the bool being in a wrapper, so the field is interpreted as an integer in the flag which implies a counting of the number flags for historical reasons and to support some particular use cases. In any case as part of that it assigns a zero to the variable. I am looking into possible solutions.