Create an insertion-ordered hash set using the provided equals and hashCode.
The provided equals must define a stable equivalence relation, and
hashCode must be consistent with equals. If the equals or hashCode
methods won't work on all objects, but only on some instances of E, the
isValidKey predicate can be used to restrict the keys that the functions
are applied to.
Any key for which isValidKey returns false is automatically assumed
to not be in the set when asking contains
.
If equals or hashCode are omitted, the set uses the elements' intrinsic Object.operator== and Object.hashCode, and isValidKey is ignored since these operations are assumed to work on all objects.
If you supply one of equals and hashCode, you should generally also to supply the other.
If the supplied equals
or hashCode
functions won't work on all E
objects, and the map will be used in a setting where a non-E
object
is passed to, e.g., contains
, then the isValidKey function should
also be supplied.
If isValidKey is omitted, it defaults to testing if the object is an E instance. That means that:
new LinkedHashSet<int>(equals: (int e1, int e2) => (e1 - e2) % 5 == 0,
hashCode: (int e) => e % 5)
does not need an isValidKey
argument, because it defaults to only
accepting int
values which are accepted by both equals
and hashCode
.
If neither equals
, hashCode
, nor isValidKey
is provided,
the default isValidKey
instead accepts all values.
The default equality and hashcode operations are assumed to work on all
objects.
Likewise, if equals
is identical, hashCode
is identityHashCode
and isValidKey
is omitted, the resulting set is identity based,
and the isValidKey
defaults to accepting all keys.
Such a map can be created directly using LinkedHashSet.identity.