You don't need to use nsIEditor, nsIPlaintextEditor and nsIHTMLEditor in most places of native code

[Masayuki Nakano]

Hi,

I was working on making editor users use concrete classes rather than
interface classes in a couple of weeks.

As I posted 2 months ago, editor concrete classes are now
mozilla::EditorBase, mozilla::TextEditor and mozilla::HTMLEditor (old
names are nsEditor, nsPlaintextEditor and nsHTMLEditor). Their header
files were already exposed. However, some users kept treating editors
with nsIEditor, nsIPlaintextEditor and nsIHTMLEditor interfaces because
they can be implemented with JS. Fortunately, we succeeded to make them
to builtinclasses [1]. So, you don't need to treat editors with
interfaces anymore in native code.

So, please do not use nsI*Editor anymore in new code. Please use
EditorBase, TextEditor or HTMLEditor classes directly. Then, you can
call non-virtual methods of editors and get the result as return value
instead of out param.

However, there is an exception. If you need to write scriptable method
which gets/sets editor from/to JS, you still need to use nsI*Editor.
When type of pointer is nsIEditor, you can retrieve pointer to concrete
classes easily and safely:

NS_IMETHODIMP
Foo::DoSomething(nsIEditor* aEditor)
{
// EditorBase is base class of any type of editors.
// However, perhaps, you don't need to use this type.
EditorBase* editorBase = aEditor->AsEditorBase();

// TextEditor is plaintext editor class and super class of
// HTMLEditor. This won't be nullptr.
TextEditor* textEditor = aEditor->AsTextEditor();

// HTMLEditor is a subclass of TextEditor. If the instance
// is an HTMLEditor, this returns non-nullptr. Otherwise, i.e.,
// it's a TextEditor instance, returns nullptr.
HTMLEditor* htmlEditor = aEditor->AsHTMLEditor();
...
}

If type of pointer is nsIPlaintextEditor or nsIHTMLEditor, you need to
QI to nsIEditor first. So, if you need to add new scriptable method
which treat editor, using nsIEditor is better than other editor
interfaces since QI cost is not so cheap.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1060051

--
Masayuki Nakano <masa...@d-toybox.com>
Software Engineer, Mozilla