Static Extension Meta Functions

proposals/0000-static-extension-meta-functions.md

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+# Static Extension Meta Functions
+
+* Proposal: [HXP-NNNN](NNNN-static-extension-meta-functions.md)
+* Author: [lublak](https://github.com/lublak)
+
+## Introduction
+
+Allow the possibility to use the meta function,
+based on the abstraction, also in static extension classes.
+
+## Motivation
+
+Currently, operator overloading, implicit casts
+and array access are reserved for abstractions only.
+However, it would also be very practical to provide this possibility via static extension classes,
+which can then be consulted with using.
+
+Just one example of how the respective functions could look:
+
+```haxe
+class UsingWithMetaFunction {
+	@:to public static inline function to(str:String):Int {
+		return Std.parseInt(str);
+	}
+
+	@:from public static function from(i:Int):String {
+		return Std.string(i);
+	}
+
+	@:op(A-B) public static inline function sub(str:String, i:Int) {
+		return str.substr(0, -i);
+	}
+
+	@:arrayAccess
+	public static inline function get(str:String, key:Int):Int {
+		return str.charCodeAt(key);
+	}
+	@:arrayAccess
+	public static inline function set(str:String, k:Int, v:Int):String {
+		return str.substring(0, k) + String.fromCharCode(v) + str.substring(k+1);
+	}
+}
+```
+
+## Detailed design
+
+Basically, the implementation could work via a kind of lookup.
+If an operator, an implicister cast to a type or an array acces occurs, it checks if the functions that have been included by using contain the respective meta.
+If so, the respective function should be called.
+
+## Impact on existing code
+
+Basically, nothing should break.
+But should someone use the meta data in these classes for other information problems could occur here.
+
+## Drawbacks
+
+None.
+
+## Alternatives
+
+Basically, the class can be wrapped with an abstract.
+But then you lose the functionalities of a class. (As an example: extends)
+
+## Unresolved questions
+
+None.