wiki:Types/Option

Option

It is an either-of algebraic type. It is either Something (a value) or Nothing (no value).

enum Option<T> {
    Some(T),
    None,
}

Just this, type-tagget mutually exclusive variants only. No monadic bullshit.

The zero-value of a type is the same core concept - there is a zero which stands for nothing (a result of 1 - 1).

There is no shortage of various option types. The dogma (or meme) behind them is to avoid null-propagation. A well-defined zero-value for each type (as in Go is the right way.

The most famous type is, of course, a Maybe.

data  Maybe a  =  Nothing | Just a

If we implement the monad interface we would have a Maybe Monad

instance  Monad Maybe  where
    (Just x) >>= k      = k x
    Nothing  >>= _      = Nothing

    (>>) = (*>)

    fail _              = Nothing

where

    Just _m1 *> m2      = m2
    Nothing  *> _m2     = Nothing

Or just simply an enumeration of variants

enum Option<T> {
     None,
     Some(T),
}
Last modified 2 years ago Last modified on Dec 6, 2018, 6:29:04 AM
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