no_member_semantics.md

Member Interceptors semantics without Member

This document is a suplement of the member interceptors proposal. The initial proposal uses a const class Member to make it easy to pass data from the system to the interceptor. This document explains the same semantics but if the contents of Member are inlined directly in the intercepting API.

Semantics

A redirecting member declaration is either:

• a redirecting field declaration
• a redirecting method declaration
• a redirecting getter declaration
• a redirecting setter declaration

A redirecting field declaration

var memberName >> constObjectExpression  [= e];

is equivalent to the declarations

_f = e;
get memberName => constObjectExpression.get(target, #memberName, _g, _s);
set memberName(v) => constObjectExpression.set(target, #memberName, v,  _g, _s);

where:

• constObjectExpression denotes a compile time constant object.
• The name _f is inaccessible to any Dart program.
• target is the receiver of the invocation (this) if it was an instance member access, otherwise it is null.
• _g is an implicitly defined static function static _g(rcvr) => rcvr._f;
• _s is an implicitly defined static function static _s(rcvr, v) => rcvr._f = v;

This implies that attempting to set a final field fails dynamically.

A redirecting getter declaration

get memberName >> constObjectExpression functionBody;

is equivalent to the getter declaration

get memberName => constObjectExpression.get(target, #memberName, _g, _s);

where:

constObjectName denotes a compile time constant object.

Throughout this section, we assume constObjectExpression supports the following API (or possibly subsets thereof, TBD):

 abstract class Interceptor {
  get(target, name, getter, setter);
  set(target, name, value, getter, setter);
  invoke(target, name, positionalArguments, namedArguments, original);
}

• target is the receiver of the invocation (this) if it was an instance member access, otherwise it is null.
• _g is an implicitly defined static function static _g(rcvr) => rcvr.__g; where __g is an implicitly defined getter function get __g functionBody implicitly defined in the same scope as memberName.
• _s is an implicitly defined static function static _s(rcvr, v) => rcvr.__s = v; where __s is an implicitly defined setter function defined as follows:
  • If memberName= is a redirecting setter, __s is the implicit setter whose body is defined by the function body given for memberName=.
  • If memberName= is an ordinary setter, __s is memberName=.
  • If no setter memberName= exists, __s is undefined and invoking it causes a runtime error.

A redirecting setter declaration

set memberName(v) >> constObjectExpression functionBody;

is equivalent to the setter declaration

set memberName(v) => constObjectExpression.set(target, #memberName, v,  _g, _s);

where:

• constObjectExpression denotes a compile time constant object.
• target is the receiver of the invocation (this) if it was an instance member access, otherwise it is null.
• _g is an implicitly defined static function static _g(rcvr) => rcvr.__g; where __g is an implicitly defined s follows:
  • If memberName is a redirecting getter, __g is the implicit getter whose body is defined by the function body given for memberName.
  • If memberName is an ordinary getter, __g is memberName.
  • If no getter memberName exists, __g is undefined and invoking it causes a runtime error.

_s is an implicitly defined static function static _s(rcvr, v) => rcvr.__s = v; where __s is an implicitly defined setter function set __s(v) functionBody implicitly defined in the same scope as memberName.

A redirecting method declaration

memberName(args) >> constObjectExpression functionBody;

is equivalent to the method declaration

memberName => constObjectExpression.invoke(target, #memberName, positionalArgs, namedArgs, _m);

where:

• constObjectExpression denotes a compile time constant object.
• target is the receiver of the invocation (this) if it was an instance member access, otherwise it is null.
• positionalArgs describes the positional arguments given in the actual invocation of the method.
• namedArgs describes the named arguments given in the actual invocation of the method.
• _m is an implicitly defined static function static _m(rcvr, args) => rcvr.__m(args); where __m is a function __m(args) {functionBody} implicitly defined in the same scope as memberName.