boolean-options.md
In Rapp: Easily Build Command Line Applications

Boolean Option Behavior

Logical defaults become boolean command-line inputs. Help output shows the most useful spelling for changing the default, while parsing also accepts explicit boolean values for convenience.

Help output is intentionally narrower than parsing. For example, foo <- TRUE normally shows --no-foo, but --foo=false is still accepted because it is an explicit boolean value for foo.

In the table below, TRUE, FALSE, and NA are the resulting R values. reject means the command-line form is not accepted.

| R definition | Help shows | Omitted | --foo | --no-foo | --foo=true | --foo=false | --foo true | --foo false | | --------------------------------------------- | ------------------ | ------: | ------: | ---------: | -----------: | ------------: | -----------: | ------------: | | foo <- FALSE | --foo | FALSE | TRUE | FALSE | TRUE | FALSE | TRUE | FALSE | | foo <- TRUE | --no-foo | TRUE | TRUE | FALSE | TRUE | FALSE | TRUE | FALSE | | foo <- NA | --foo / --no-foo | NA | TRUE | FALSE | TRUE | FALSE | TRUE | FALSE | | #\| negative_alias: falsefoo <- FALSE | --foo | FALSE | TRUE | reject | TRUE | FALSE | TRUE | FALSE | | #\| negative_alias: falsefoo <- TRUE | --foo <FOO> | TRUE | TRUE | reject | TRUE | FALSE | TRUE | FALSE | | #\| negative_alias: falsefoo <- NA | --foo | NA | TRUE | reject | TRUE | FALSE | TRUE | FALSE | | #\| arg_type: optionfoo <- NA | --foo <FOO> | NA | reject | reject | TRUE | FALSE | TRUE | FALSE |

Bare --foo and --no-foo count as supplied values for boolean switches. Use #| arg_type: option when a boolean input should require an explicit value after --foo.

#| negative_alias: false only disables the generated --no-foo spelling. It does not disable the positive spelling or explicit value forms such as --foo=false. With foo <- TRUE, that leaves no default-changing bare alias, so help shows --foo <FOO> as an explicit-value form.