[2.5] Added the Valiator method isBoolean

[ghost]

No description provided.

[GrahamCampbell]

Thanks for the PR. Our variables are always strings though sent they?

[ghost]

Yes all values are in the format of strings this method ensures they are in the format accepted as booleans - Yes, No, 1, 0, On and Off

[danhunsaker]

Has some weird indentation, but otherwise it looks sound.

[jpuck]

I like it. It uses simple built-ins, but in my opinion there is one non-intuitive condition with filter_var and FILTER_NULL_ON_FAILURE which returns FALSE on the empty string "" which I don't think makes sense with dotenv (but maybe it does).

There needs to be some unit tests to accompany changes, and there's some minor whitespace consistency issues.

I submitted a pull request which should resolve all these issues.

Furthermore, while probably out of scope, it might be worth considering other edge cases such as (true) like it's handled in the laravel framework.

[jpuck]

whoops, looks like the tests are not compatible with ye olde php 5.3
I'll update that to use the formal array() instead of []

fixed in https://github.com/sephedo/phpdotenv/pull/2

build: https://travis-ci.org/scratchers/phpdotenv/builds/198163739

[jamesj2]

It's been a year. Any possibility of this getting merged?

[vlucas]

This looks pretty solid to me. Has tests and will not affect anyone if they are not using the boolean validator.