patch 9.0.1001: classes are not documented or implemented yet

Problem:    Classes are not documented or implemented yet.
Solution:   Make the first steps at documenting Vim9 objects, classes and
            interfaces.  Make initial choices for the syntax.  Add a skeleton
            implementation.  Add "public" and "this" in the command table.

Filelist

@@ -163,6 +163,7 @@ SRC_ALL =	\
 		src/version.h \
 		src/vim.h \
 		src/vim9.h \
+		src/vim9class.c \
 		src/vim9cmds.c \
 		src/vim9compile.c \
 		src/vim9execute.c \
@@ -327,6 +328,7 @@ SRC_ALL =	\
 		src/proto/usercmd.pro \
 		src/proto/userfunc.pro \
 		src/proto/version.pro \
+		src/proto/vim9class.pro \
 		src/proto/vim9cmds.pro \
 		src/proto/vim9compile.pro \
 		src/proto/vim9execute.pro \

runtime/doc/Makefile

@@ -161,6 +161,7 @@ DOCS = \
 	version9.txt \
 	vi_diff.txt \
 	vim9.txt \
+	vim9class.txt \
 	visual.txt \
 	windows.txt \
 	workshop.txt
@@ -313,6 +314,7 @@ HTMLS = \
 	vi_diff.html \
 	vimindex.html \
 	vim9.html \
+	vim9class.html \
 	visual.html \
 	windows.html \
 	workshop.html

runtime/doc/vim9.txt

@@ -16,7 +16,7 @@ features in Vim9 script.
 3.  New style functions			|fast-functions|
 4.  Types				|vim9-types|
 5.  Namespace, Import and Export	|vim9script|
-6.  Future work: classes		|vim9-classes|
+6.  Classes and interfaces		|vim9-classes|
 
 9.  Rationale				|vim9-rationale|
 
@@ -1940,73 +1940,17 @@ Or: >
 
 ==============================================================================
 
-6. Future work: classes					*vim9-classes*
-
-Above "class" was mentioned a few times, but it has not been implemented yet.
-Most of Vim9 script can be created without this functionality, and since
-implementing classes is going to be a lot of work, it is left for the future.
-For now we'll just make sure classes can be added later.
-
-Thoughts:
-- `class` / `endclass`, the whole class must be in one file
-- Class names are always CamelCase (to avoid a name clash with builtin types)
-- A single constructor called "constructor" (similar to TypeScript)
-- Single inheritance: `class ThisClass extends BaseClass`
-- `interface` / `endinterface` (looks like a class without any implementation)
-- Explicit declaration that the class supports an interface, so that type
-  checking works properly:
-  `class SomeClass implements SomeInterface, OtherInterface`
-- `abstract class` (class with incomplete implementation) - not really needed?
-- Class (static) methods and Object methods: syntax to be defined.
-- Class (static) members and Object members: syntax to be defined.
-- Access control: private / protected / shared / public ?  Keep it simple.
-- Access object members with `this.member` ?
-- Generics for class: `class <Tkey, Tentry>`
-- Generics for function: `def <Tkey> GetLast(key: Tkey)`
-- Method overloading (two methods with the same name but different argument
-  types): Most likely not
-- Mixins: not sure if that is useful, leave out for simplicity.
-
-Again, much of this is from TypeScript with a slightly different syntax.
-
-Some things that look like good additions:
-- Use a class as an interface (like Dart)
-- Extend a class with methods, using an import (like Dart)
-- Mixins
-- For testing: Mock mechanism
-
-An important class that will be provided is "Promise".  Since Vim is single
-threaded, connecting asynchronous operations is a natural way of allowing
-plugins to do their work without blocking the user.  It's a uniform way to
-invoke callbacks and handle timeouts and errors.
-
-Some commands have already been reserved:
-	*:class*
-	*:endclass*
-	*:abstract*
-	*:enum*
-	*:endenum*
-	*:interface*
-	*:endinterface*
-	*:static*
-	*:type*
-
-Some examples: >
-
-	abstract class Person
-	    static const prefix = 'xxx'
-	    var name: string
-
-	    def constructor(name: string)
-		this.name = name
-	    enddef
-
-	    def display(): void
-		echo name
-	    enddef
-
-	    abstract def find(string): Person
-	endclass
+6. Classes and interfaces				*vim9-classes*
+
+In legacy script a Dictionary could be used as a kind-of object, by adding
+members that are functions.  However, this is quite inefficient and requires
+the writer to do the work of making sure all the objects have the right
+members.  See |Dictionary-function|.
+
+In |Vim9| script you can have classes, objects and interfaces like in most
+popular object-oriented programming languages.  Since this is a lot of
+functionality it is located in a separate help file: |vim9class.txt|.
+
 
 ==============================================================================
 
@@ -2293,18 +2237,5 @@ tool need to be supported.  Since most languages support classes the lack of
 support for classes in Vim is then a problem.
 
 
-Classes ~
-
-Vim supports a kind-of object oriented programming by adding methods to a
-dictionary.  With some care this can be made to work, but it does not look
-like real classes.  On top of that, it's quite slow, because of the use of
-dictionaries.
-
-It would be good to support real classes, and this is planned for a later
-version.  The support is a "minimal common functionality" of class support in
-most languages.  It will work much like Java, which is the most popular
-programming language.
-
-
 
  vim:tw=78:ts=8:noet:ft=help:norl: