Method cast

src/main/java/net/starlark/java/eval/Dict.java:659–684

Casts a non-null Starlark value x to a Dict after checking that all keys and values are instances of keyType and valueType, respectively. On error, it throws an EvalException whose message includes what, ideally a string literal, as a description of the

(Object x, Class<K> keyType, Class<V> valueType, String what)

   * description of the role of {@code x}. If x is null, it returns an immutable empty dict.
   */
  public static <K, V> Dict<K, V> cast(Object x, Class<K> keyType, Class<V> valueType, String what)
      throws EvalException {
    Preconditions.checkNotNull(x);
    if (!(x instanceof Dict)) {
      throw Starlark.errorf("got %s for '%s', want dict", Starlark.type(x), what);
    }

    for (Map.Entry<?, ?> e : ((Map<?, ?>) x).entrySet()) {
      if (!keyType.isAssignableFrom(e.getKey().getClass())
          || !valueType.isAssignableFrom(e.getValue().getClass())) {
        // TODO(adonovan): change message to "found <K2, V2> entry",
        // without suggesting that the entire dict is <K2, V2>.
        throw Starlark.errorf(
            "got dict<%s, %s> for '%s', want dict<%s, %s>",
            Starlark.type(e.getKey()),
            Starlark.type(e.getValue()),
            what,
            Starlark.classType(keyType),
            Starlark.classType(valueType));
      }
    }

    @SuppressWarnings("unchecked") // safe
    Dict<K, V> res = (Dict<K, V>) x;
    return res;
  }

  /** Like {@link #cast}, but if x is None, returns an empty Dict. */
  public static <K, V> Dict<K, V> noneableCast(