Beispiel #1
0
  /**
   * Remember that we are trying to cast something of type {@code supertype} to {@code subtype}.
   *
   * <p>Since at runtime we can only check the class (type constructor), the rest of the subtype
   * should be known statically, from supertype. This method reconstructs all static information
   * that can be obtained from supertype.
   *
   * <p>Example 1: supertype = Collection<String> subtype = List<...> result = List<String>, all
   * arguments are inferred
   *
   * <p>Example 2: supertype = Any subtype = List<...> result = List<*>, some arguments were not
   * inferred, replaced with '*'
   */
  public static TypeReconstructionResult findStaticallyKnownSubtype(
      @NotNull JetType supertype, @NotNull TypeConstructor subtypeConstructor) {
    assert !supertype.isNullable() : "This method only makes sense for non-nullable types";

    // Assume we are casting an expression of type Collection<Foo> to List<Bar>
    // First, let's make List<T>, where T is a type variable
    ClassifierDescriptor descriptor = subtypeConstructor.getDeclarationDescriptor();
    assert descriptor != null : "Can't create default type for " + subtypeConstructor;
    JetType subtypeWithVariables = descriptor.getDefaultType();

    // Now, let's find a supertype of List<T> that is a Collection of something,
    // in this case it will be Collection<T>
    JetType supertypeWithVariables =
        TypeCheckingProcedure.findCorrespondingSupertype(subtypeWithVariables, supertype);

    final List<TypeParameterDescriptor> variables =
        subtypeWithVariables.getConstructor().getParameters();

    Map<TypeConstructor, TypeProjection> substitution;
    if (supertypeWithVariables != null) {
      // Now, let's try to unify Collection<T> and Collection<Foo> solution is a map from T to Foo
      TypeUnifier.UnificationResult solution =
          TypeUnifier.unify(
              new TypeProjectionImpl(supertype),
              new TypeProjectionImpl(supertypeWithVariables),
              new Predicate<TypeConstructor>() {
                @Override
                public boolean apply(TypeConstructor typeConstructor) {
                  ClassifierDescriptor descriptor = typeConstructor.getDeclarationDescriptor();
                  return descriptor instanceof TypeParameterDescriptor
                      && variables.contains(descriptor);
                }
              });
      substitution = Maps.newHashMap(solution.getSubstitution());
    } else {
      // If there's no corresponding supertype, no variables are determined
      // This may be OK, e.g. in case 'Any as List<*>'
      substitution = Maps.newHashMapWithExpectedSize(variables.size());
    }

    // If some of the parameters are not determined by unification, it means that these parameters
    // are lost,
    // let's put stars instead, so that we can only cast to something like List<*>, e.g. (a: Any) as
    // List<*>
    boolean allArgumentsInferred = true;
    for (TypeParameterDescriptor variable : variables) {
      TypeProjection value = substitution.get(variable.getTypeConstructor());
      if (value == null) {
        substitution.put(
            variable.getTypeConstructor(), SubstitutionUtils.makeStarProjection(variable));
        allArgumentsInferred = false;
      }
    }

    // At this point we have values for all type parameters of List
    // Let's make a type by substituting them: List<T> -> List<Foo>
    JetType substituted =
        TypeSubstitutor.create(substitution).substitute(subtypeWithVariables, Variance.INVARIANT);

    return new TypeReconstructionResult(substituted, allArgumentsInferred);
  }