ceylon.language.meta.declaration.Variance.ceylon Maven / Gradle / Ivy

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"Variance information."
shared interface Variance of invariant | covariant | contravariant {}

"Invariant means that neither subtype nor supertype can be accepted, the
 type has to be exactly that which is declared."
shared object invariant satisfies Variance {
    string => "Invariant";
}

"Covariant means that subtypes of the given type may be returned."
shared object covariant satisfies Variance {
    string => "Covariant";
}

"Contravariant means that supertypes of the given type may be accepted."
shared object contravariant satisfies Variance {
    string => "Contravariant";
}