Collections library: supporing immutable part of interfaces.

[DartBot]

This issue was originally filed by karl.k...@gmail.com

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In Java, the interfaces in the collections library allow that implementors only implement the read-only part of the interface throwing UnsupportedOperationException when calling the mutating part.

The Dart interfaces don't explicitly say this. I believe they should, as it allows implementing immutable collection types that implement the Dart collections interfaces.

For example, one might change

interface List<E> extends Collection<E> factory ListFactory {
//...

  /**
   * Sets the entry at the given [index] in the list to [value].
   * Throws an [IndexOutOfRangeException] if [index] is out of bounds.
   */
  void operator []=(int index, E value);
//...
}

to

interface List<E> extends Collection<E> factory ListFactory {
//...

  /**
   * Sets the entry at the given [index] in the list to [value].
   * Throws an [IndexOutOfRangeException] if [index] is out of bounds.
   * Throws an [UnsupportedOperationException] if the list is immutable.
   */
  void operator []=(int index, E value);
//...
}

etc.

[DartBot]

This comment was originally written by drfibonacci@google.com

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Added Area-Library, Triaged labels.

[lrhn]

I believe this has been documented in the base collection classes now.
An unmodifiable List will throw UnsupportedError for mutating methods.

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Added Fixed label.