implement either :one, :two

[alezummo]

Makes at least one of the opts required, but fails if both or none are given.

[Fryguy]

LGTM - a small comment about preferring interpolation over concatenation. @kbrock Please also review.

[nanobowers]

This seems like a specialization of a more general type of argument validation.

More specifically, the condition you are trying to satisfy with either: is max==1 and min==1. Should we entertain cases where min/max are not 1? conflicts: is kinda like max==1 and min==ANY

Was thinking something along the lines of:

validate min: <Integer/nil>, max: <Integer/nil>, args: <Array of Symbol>

Another related thought - @Fryguy should there any default notation in the help message for exclusivity clauses? If the developer uses either:, conflicts: or depends, seems like the only good way to find out is to try it and get an error message, or the developer would have to manually note it with the banner message.

[Fryguy]

While it might be nice to have a general case, that doesn't preclude having specialized methods, which are readable, and can later be implemented in terms of the generic code. conflicts :bar, :baz is probably clearer than something like constraint :bar, :baz, min: 1, max: :any.

For the help text I was thinking the same thing, but since depends and conflicts don't currently do that, then I don't think it should hold up this PR. I'm also not exactly sure how one would implement that.

[alezummo]

I particularly liked the elegance of writing either instead of a more convoluted syntax.

[kbrock]

I noticed there are no tests for the happy path.

Amusingly, typically people just test the working code and forget to test the problems. Seems you have done the opposite.

Just add a working example and then lets shipit

[Fryguy]

@kbrock I think the test lines that are calling .parse, but not wrapped in assert_raises are the happy path. i.e. https://github.com/ManageIQ/optimist/pull/130/files#diff-2ba0f24469c763ceb2f38630ff0526bef69b594e08daa3c1bcd12889a14141beR771-R772 and https://github.com/ManageIQ/optimist/pull/130/files#diff-2ba0f24469c763ceb2f38630ff0526bef69b594e08daa3c1bcd12889a14141beR785-R788

[kbrock]

@Fryguy LGTM. merge if you are all set