Implemented connectable port

src/core/port.ts

@@ -7,7 +7,8 @@ import type {
   Absent,
   MultiReadWrite,
   ReadWrite,
-  Variable
+  Variable,
+  Read
 } from "./internal";
 import {Trigger, Log} from "./internal";
 
@@ -59,6 +60,15 @@ export abstract class Port<T> extends Trigger {
   }
 }
 
+export class ConnectablePort<T> implements Read<T> {
+  public get = (): Absent => (undefined);
+  public getPort = (): IOPort<T> => (this.port);
+
+  constructor (
+    public port: IOPort<T>
+  ) {}
+}
+
 /**
  * Abstract class for a writable port. It is intended as a wrapper for a
  * regular port. In addition to a get method, it also has a set method and
@@ -103,6 +113,10 @@ export abstract class IOPort<T> extends Port<T> {
     }
   }
 
+  public asConnectable(): ConnectablePort<T> {
+    return new ConnectablePort(this);
+  }
+
   /**
    * Only the holder of the key may obtain a writable port.
    * @param key

src/core/reactor.ts

@@ -42,7 +42,7 @@ import {
   Startup,
   Shutdown,
   WritableMultiPort,
-  Dummy
+  Dummy, ConnectablePort
 } from "./internal";
 import {v4 as uuidv4} from "uuid";
 import {Bank} from "./bank";
@@ -474,20 +474,20 @@ export abstract class Reactor extends Component {
      * @param dst
      */
 
-    public connect<R, S extends R>(src: IOPort<S>, dst: IOPort<R>): void;
+    public connect<R, S extends R>(src: ConnectablePort<S>, dst: ConnectablePort<R>): void;
     public connect<A extends T, R, T, S extends R>(
       src: CallerPort<A, R>,
       dst: CalleePort<T, S>
     ): void;
     public connect<A extends T, R, T, S extends R>(
       ...[src, dst]:
-        | [IOPort<S>, IOPort<R>]
+        | [ConnectablePort<S>, ConnectablePort<R>]
         | [CallerPort<A, R>, CalleePort<T, S>]
     ): void {
       if (src instanceof CallerPort && dst instanceof CalleePort) {
         this.reactor._connectCall(src, dst);
-      } else if (src instanceof IOPort && dst instanceof IOPort) {
-        this.reactor._connect(src, dst);
+      } else if (src instanceof ConnectablePort && dst instanceof ConnectablePort) {
+        this.reactor._connect(src.getPort(), dst.getPort());
       } else {
         throw Error(
           "Logically unreachable code: src and dst type mismatch, Caller(ee) port cannot be connected to IOPort."
@@ -1850,7 +1850,7 @@ interface UtilityFunctions {
 
 export interface MutationSandbox extends ReactionSandbox {
   connect: {
-    <R, S extends R>(src: IOPort<S>, dst: IOPort<R>): void;
+    <R, S extends R>(src: ConnectablePort<S>, dst: ConnectablePort<R>): void;
     <A extends T, R, T, S extends R>(
       src: CallerPort<A, R>,
       dst: CalleePort<T, S>