feat(core): Fn.ref (#5468)

packages/@aws-cdk/core/lib/cfn-fn.ts

@@ -13,6 +13,15 @@ import { Token } from './token';
  * http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference.html
  */
 export class Fn {
+  /**
+   * The ``Ref`` intrinsic function returns the value of the specified parameter or resource.
+   * Note that it doesn't validate the logicalName, it mainly serves paremeter/resource reference defined in a ``CfnInclude`` template.
+   * @param logicalName The logical name of a parameter/resource for which you want to retrieve its value.
+   */
+  public static ref(logicalName: string): string {
+    return new FnRef(logicalName).toString();
+  }
+
   /**
    * The ``Fn::GetAtt`` intrinsic function returns the value of an attribute
    * from a resource in the template.
@@ -311,6 +320,21 @@ class FnBase extends Intrinsic {
   }
 }
 
+/**
+ * The intrinsic function ``Ref`` returns the value of the specified parameter or resource.
+ * When you specify a parameter's logical name, it returns the value of the parameter.
+ * When you specify a resource's logical name, it returns a value that you can typically use to refer to that resource, such as a physical ID.
+ */
+class FnRef extends FnBase {
+  /**
+   * Creates an ``Ref`` function.
+   * @param logicalName The logical name of a parameter/resource for which you want to retrieve its value.
+   */
+  constructor(logicalName: string) {
+    super('Ref', logicalName);
+  }
+}
+
 /**
  * The intrinsic function ``Fn::FindInMap`` returns the value corresponding to keys in a two-level
  * map that is declared in the Mappings section.

packages/@aws-cdk/core/test/test.fn.ts

@@ -168,6 +168,15 @@ export = nodeunit.testCase({
       });
     }),
   },
+  'Ref': {
+    'returns a reference given a logical name'(test: nodeunit.Test) {
+      const stack = new Stack();
+      test.deepEqual(stack.resolve(Fn.ref('hello')), {
+        Ref: 'hello'
+      });
+      test.done();
+    }
+  }
 });
 
 function stringListToken(o: any): string[] {