patch 9.0.2167: Vim9: not consistently using :var for declarations

Problem:  Vim9-script object/class variable declarations use syntax
	  that is inconsistent with the rest of the language.
Solution: Use :var to declare object and class variables.

closes: #13670

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/vim9class.txt

@@ -78,8 +78,8 @@ Let's start with a simple example: a class that stores a text position (see
 below for how to do this more efficiently): >
 
 	class TextPosition
-	   this.lnum: number
-	   this.col: number
+	   var lnum: number
+	   var col: number
 
 	   def new(lnum: number, col: number)
 	      this.lnum = lnum
@@ -156,8 +156,8 @@ On the other hand, if you do not want the object variables to be read directly
 from outside the class or its sub-classes, you can make them protected.  This
 is done by prefixing an underscore to the name: >
 
-	this._lnum: number
-	this._col number
+	var _lnum: number
+	var _col number
 
 Now you need to provide methods to get the value of the protected variables.
 These are commonly called getters.  We recommend using a name that starts with
@@ -209,8 +209,8 @@ Many constructors take values for the object variables.  Thus you very often
 see this pattern: >
 
 	 class SomeClass
-	   this.lnum: number
-	   this.col: number
+	   var lnum: number
+	   var col: number
 
 	   def new(lnum: number, col: number)
 	      this.lnum = lnum
@@ -235,8 +235,8 @@ Putting together this way of using new() and making the variables public
 results in a much shorter class definition than what we started with: >
 
 	class TextPosition
-	   public this.lnum: number
-	   public this.col: number
+	   public var lnum: number
+	   public var col: number
 
 	   def new(this.lnum, this.col)
 	   enddef
@@ -277,8 +277,8 @@ Class members are declared with "static".  They are used by the name without a
 prefix in the class where they are defined: >
 
 	class OtherThing
-	   this.size: number
-	   static totalSize: number
+	   var size: number
+	   static var totalSize: number
 
 	   def new(this.size)
 	      totalSize += this.size
@@ -297,9 +297,9 @@ underscore as the first character in the name, and it can be made public by
 prefixing "public": >
 
     class OtherThing
-	static total: number	      # anybody can read, only class can write
-	static _sum: number	      # only class can read and write
-	public static result: number  # anybody can read and write
+	static var total: number	  # anybody can read, only class can write
+	static var _sum: number	          # only class can read and write
+	public static var result: number  # anybody can read and write
     endclass
 <
 							*class-method*
@@ -308,8 +308,8 @@ variables but they have no access to the object variables, they cannot use the
 "this" keyword:
 >
 	class OtherThing
-	   this.size: number
-	   static totalSize: number
+	   var size: number
+	   static var totalSize: number
 
 	   # Clear the total size and return the value it had before.
 	   static def ClearTotalSize(): number
@@ -345,14 +345,14 @@ outside of the defining class: >
 
     vim9script
     class Vehicle
-	static nextID: number = 1000
+	static var nextID: number = 1000
 	static def GetID(): number
 	    nextID += 1
 	    return nextID
 	enddef
     endclass
     class Car extends Vehicle
-	this.myID: number
+	var myID: number
 	def new()
 	    this.myID = Vehicle.GetID()
 	enddef
@@ -380,20 +380,20 @@ it is.  The Shape class functions as the base for a Square and a Triangle
 class, for which objects can be created.  Example: >
 
 	abstract class Shape
-	   this.color = Color.Black
-	   this.thickness = 10
+	   var color = Color.Black
+	   var thickness = 10
 	endclass
 
 	class Square extends Shape
-	   this.size: number
+	   var size: number
 
 	   def new(this.size)
 	   enddef
 	endclass
 
 	class Triangle extends Shape
-	   this.base: number
-	   this.height: number
+	   var base: number
+	   var height: number
 
 	   def new(this.base, this.height)
 	   enddef
@@ -430,16 +430,16 @@ interface called HasSurface, which specifies one method Surface() that returns
 a number.  This example extends the one above: >
 
 	abstract class Shape
-	   this.color = Color.Black
-	   this.thickness = 10
+	   var color = Color.Black
+	   var thickness = 10
 	endclass
 
 	interface HasSurface
 	   def Surface(): number
 	endinterface
 
 	class Square extends Shape implements HasSurface
-	   this.size: number
+	   var size: number
 
 	   def new(this.size)
 	   enddef
@@ -450,8 +450,8 @@ a number.  This example extends the one above: >
 	endclass
 
 	class Triangle extends Shape implements HasSurface
-	   this.base: number
-	   this.height: number
+	   var base: number
+	   var height: number
 
 	   def new(this.base, this.height)
 	   enddef
@@ -598,13 +598,13 @@ Items in a class ~
 						*E1318* *E1325* *E1388*
 Inside a class, in between `:class` and `:endclass`, these items can appear:
 - An object variable declaration: >
-	this._protectedVariableName: memberType
-	this.readonlyVariableName: memberType
-	public this.readwriteVariableName: memberType
+	var _protectedVariableName: memberType
+	var readonlyVariableName: memberType
+	public var readwriteVariableName: memberType
 - A class variable declaration: >
-	static _protectedClassVariableName: memberType
-	static readonlyClassVariableName: memberType
-	static public readwriteClassVariableName: memberType
+	static var _protectedClassVariableName: memberType
+	static var readonlyClassVariableName: memberType
+	static var public readwriteClassVariableName: memberType
 - A constructor method: >
 	def new(arguments)
 	def newName(arguments)
@@ -620,9 +620,9 @@ this explicitly with ": {type}".  For simple types you can also use an
 initializer, such as "= 123", and Vim will see that the type is a number.
 Avoid doing this for more complex types and when the type will be incomplete.
 For example: >
-	this.nameList = []
+	var nameList = []
 This specifies a list, but the item type is unknown.  Better use: >
-	this.nameList: list<string>
+	var nameList: list<string>
 The initialization isn't needed, the list is empty by default.
 							*E1330*
 Some types cannot be used, such as "void", "null" and "v:none".
@@ -646,7 +646,7 @@ An interface can declare methods with `:def`, including the arguments and
 return type, but without the body and without `:enddef`.  Example: >
 
 	interface HasSurface
-	   this.size: number
+	   var size: number
 	   def Surface(): number
 	endinterface
 
@@ -674,9 +674,9 @@ defined.  This default constructor will have arguments for all the object
 variables, in the order they were specified.  Thus if your class looks like: >
 
 	class AutoNew
-	   this.name: string
-	   this.age: number
-	   this.gender: Gender
+	   var name: string
+	   var age: number
+	   var gender: Gender
 	endclass
 
 Then the default constructor will be: >
@@ -690,8 +690,8 @@ value for the object variables will be used.  This is a more useful example,
 with default values: >
 
 	class TextPosition
-	   this.lnum: number = 1
-	   this.col: number = 1
+	   var lnum: number = 1
+	   var col: number = 1
 	endclass
 
 If you want the constructor to have mandatory arguments, you need to write it
@@ -947,36 +947,43 @@ Following that Vim object variables could be declared like this: >
 Some users pointed out that this looks more like an assignment than a
 declaration.  Adding "var" changes that: >
 	class Point
-	  var this.x: number
-	  var this.y = 0
+	  var x: number
+	  var y = 0
 	endclass
 
 We also need to be able to declare class variables using the "static" keyword.
 There we can also choose to leave out "var": >
 	class Point
-	  var this.x: number
+	  var x: number
 	  static count = 0
 	endclass
 
 Or do use it, before "static": >
 	class Point
-	  var this.x: number
+	  var x: number
 	  var static count = 0
 	endclass
 
 Or after "static": >
 	class Point
-	  var this.x: number
+	  var x: number
 	  static var count = 0
 	endclass
 
 This is more in line with "static def Func()".
 
 There is no clear preference whether to use "var" or not.  The two main
 reasons to leave it out are:
-1. TypeScript, Java and other popular languages do not use it.
+1. TypeScript and other popular languages do not use it.
 2. Less clutter.
 
+However, it is more common for languages to reuse their general variable and
+function declaration syntax for class/object variables and methods.  Vim9 also
+reuses the general function declaration syntax for methods.  So, for the sake
+of consistency, we require "var" in these declarations.
+
+This also allows for a natural use of "final" and "const" in the future.
+
 
 Using "ClassName.new()" to construct an object ~
 

src/errors.h

@@ -3402,11 +3402,12 @@ EXTERN char e_object_required_found_str[]
 	INIT(= N_("E1327: Object required, found %s"));
 EXTERN char e_constructor_default_value_must_be_vnone_str[]
 	INIT(= N_("E1328: Constructor default value must be v:none: %s"));
-// E1329 unused
+EXTERN char e_invalid_class_variable_declaration_str[]
+	INIT(= N_("E1329: Invalid class variable declaration: %s"));
 EXTERN char e_invalid_type_for_object_variable_str[]
 	INIT(= N_("E1330: Invalid type for object variable: %s"));
-EXTERN char e_public_must_be_followed_by_this_or_static[]
-	INIT(= N_("E1331: Public must be followed by \"this\" or \"static\""));
+EXTERN char e_public_must_be_followed_by_var_or_static[]
+	INIT(= N_("E1331: Public must be followed by \"var\" or \"static\""));
 EXTERN char e_public_variable_name_cannot_start_with_underscore_str[]
 	INIT(= N_("E1332: Public variable name cannot start with underscore: %s"));
 EXTERN char e_cannot_access_protected_variable_str[]
@@ -3487,8 +3488,8 @@ EXTERN char e_cannot_access_protected_method_str[]
 	INIT(= N_("E1366: Cannot access protected method: %s"));
 EXTERN char e_variable_str_of_interface_str_has_different_access[]
 	INIT(= N_("E1367: Access level of variable \"%s\" of interface \"%s\" is different"));
-EXTERN char e_static_cannot_be_followed_by_this[]
-	INIT(= N_("E1368: Static cannot be followed by \"this\" in a variable name"));
+EXTERN char e_static_must_be_followed_by_var_or_def[]
+	INIT(= N_("E1368: Static must be followed by \"var\" or \"def\""));
 EXTERN char e_duplicate_variable_str[]
 	INIT(= N_("E1369: Duplicate variable: %s"));
 EXTERN char e_cannot_define_new_method_as_static[]

src/testdir/test_vim9_builtin.vim

@@ -4845,7 +4845,7 @@ def Test_values()
       vim9script
 
       class Foo
-        this.val: number
+        var val: number
         def Add()
           echo this.val
         enddef