verifyUsageOption method
Implementation
void verifyUsageOption(String value, List<String> options) {
if(options.contains(value)) {
return;
}
final msg = StringBuffer("$value must be one of (");
for(final key in options) {
msg.write(key);
msg.write(", ");
}
msg.write(")");
throwUsageError(msg.toString());
}