First, `EditorBase::CreateTransactionForDeleteSelection` returns an instance of
`EditAggregateTransaction`. It's a base class of `PlaceholderTransaction` and
`DeleteRangeTransaction` but it's also a concrete class. However, it's too
generic. Therefore, this patch creates `DeleteMultipleRangesTransaction` which
is a simple sub-class of it, and makes `EditAggregateTransaction` be an abstract
class. Then, add `AddChild` methods to each concrete class to restrict the
type of child transactions.
Next, `DeleteRangeTransaction` contains only `DeleteNodeTransaction` and
`DeleteTextTransaction`. Therefore, once they have a common base class,
we can check the type easier. Therefore, this patch also adds
`DeleteContentTransactionBase` and
`EditorBase::CreateTransactionForCollapsedRange` becomes clearer what it
returns.
With these changes, `DeleteRangeTransaction` obviously contains only
`DeleteContentTransactionBase`, `DeleteMultipleRangesTransaction` contains only
`DeleteRangeTransaction`, `DeleteNodeTransaction` and `DeleteTextTransaction`.
And they are guaranteed at build time (at least from outside the classes).
***
fix
Differential Revision: https://phabricator.services.mozilla.com/D169038
Masayuki Nakano