framework.src.org.checkerframework.qualframework.poly.ContainmentHierarchy Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of checker Show documentation

The Checker Framework enhances Java’s type system to make it more powerful and useful. This lets software developers detect and prevent errors in their Java programs. The Checker Framework includes compiler plug-ins ("checkers") that find bugs or verify their absence. It also permits you to write your own compiler plug-ins.

There is a newer version: 3.42.0

Show newest version

package org.checkerframework.qualframework.poly;

import org.checkerframework.qualframework.base.QualifierHierarchy;

/** A hierarchy of {@link Wildcard}s, ordered by the containment relation (JLS
 * 4.5.1).
 */
public class ContainmentHierarchy implements QualifierHierarchy> {
    private QualifierHierarchy> polyQualHierarchy;

    /**
     * @param polyQualHierarchy  the hierarchy to use for comparing wildcard bounds
     */
    public ContainmentHierarchy(QualifierHierarchy> polyQualHierarchy) {
        this.polyQualHierarchy = polyQualHierarchy;
    }

    @Override
    public boolean isSubtype(Wildcard subtype, Wildcard supertype) {
        if (subtype.isEmpty()) {
            return true;
        }

        if (supertype.isEmpty()) {
            return false;
        }

        // We consider SUB to be a subtype of SUPER if SUB is contained by
        // SUPER.  SUPER contains SUB if the bounds of SUPER lie outside the
        // bounds of SUB.
        return polyQualHierarchy.isSubtype(supertype.getLowerBound(), subtype.getLowerBound())
            && polyQualHierarchy.isSubtype(subtype.getUpperBound(), supertype.getUpperBound());
    }

    @Override
    public Wildcard leastUpperBound(Wildcard a, Wildcard b) {
        if (a.isEmpty()) {
            return b;
        }

        if (b.isEmpty()) {
            return a;
        }

        // Take the more permissive input for each bound, to produce a new
        // wildcard that contains both `a` and `b`.
        return new Wildcard(
                polyQualHierarchy.greatestLowerBound(a.getLowerBound(), b.getLowerBound()),
                polyQualHierarchy.leastUpperBound(a.getUpperBound(), b.getUpperBound()));
    }

    @Override
    public Wildcard greatestLowerBound(Wildcard a, Wildcard b) {
        if (a.isEmpty()) {
            return a;
        }

        if (b.isEmpty()) {
            return b;
        }

        PolyQual newLower = polyQualHierarchy.leastUpperBound(a.getLowerBound(), b.getLowerBound());
        PolyQual newUpper = polyQualHierarchy.greatestLowerBound(a.getUpperBound(), b.getUpperBound());

        if (!polyQualHierarchy.isSubtype(newLower, newUpper)) {
            return Wildcard.empty();
        } else {
            return new Wildcard(newLower, newUpper);
        }
    }

    @Override
    public Wildcard getTop() {
        return new Wildcard(polyQualHierarchy.getBottom(), polyQualHierarchy.getTop());
    }

    @Override
    public Wildcard getBottom() {
        return Wildcard.empty();
    }
}