Method Equals

Gives true when the given object is a Maybe<T> of this type equal to this one.

public override bool Equals(object? obj)

bool: true if obj is a Maybe<T> of the same type which operator ==(Maybe<T>, Maybe<T>) considers equal to this one.

A Maybe<T> is never equal to the bare value it contains, only to a second Maybe<T>.

Gives true when the given instance is equal to this one.

public bool Equals(Maybe<T> other)

The same compare as operator ==(Maybe<T>, Maybe<T>), with the name Default looks for. Without it, this struct has no IEquatable<T> and sends each compare through Equals(object?), which boxes the two operands. That occurs on each Distinct<TSource>(IEnumerable<TSource>) , Contains<TSource>(IEnumerable<TSource>, TSource) , IndexOf(T), and dictionary lookup. A struct is how this type avoids an allocation, and that made it allocate in the collection-heavy code that notices.