www.dictionary.com/browse/optional

Optional definition, left to one's choice; not required or mandatory: Formal dress is optional. See more.

dictionary.cambridge.org/us/dictionary/english/optional

optional meaning: 1. If something is optional, you can choose if you want to do it, pay it, buy it, etc.: 2. not necessary or demanded but possible or available; ...

www.merriam-webster.com/dictionary/optional

Optional definition is - involving an option : not compulsory. How to ... See the full definition for optional in the English Language Learners Dictionary. optional.

www.macmillandictionary.com/us/dictionary/american/optional

Define optional (adjective) and get synonyms. What is optional (adjective)? optional (adjective) meaning, pronunciation and more by Macmillan Dictionary.

www.ldoceonline.com/dictionary/optional

optional meaning, definition, what is optional: if something is optional, you do not hav...: Learn more.

www.collinsdictionary.com/us/dictionary/english/optional

Optional definition: If something is optional , you can choose whether or not you do it or have it. | Meaning, pronunciation, translations and examples.

www.vocabulary.com/dictionary/optional

optional. If you can choose whether or not to do something, it is optional. Extra credit is always optional; death and taxes are not. When you buy a new car, you ...

www.urbandictionary.com/define.php?term=Optional

Not mandatory; A decision can be made in this situation.

stackoverflow.com/questions/44982414/dictionary-of-optional-keys

This allowed for Optional to be made conditionally Hashable , when ... So you can use any Optional<T: Hashable> as a dictionary key, directly!