'abstract' keyword no longer required for interface method declarations

- A warning is not yet being thrown for redundancy if the abstract keyword is
  explicitly specified

README.md

@@ -209,12 +209,12 @@ be considered abstract and must be declared as such.
 
 ### Interfaces
 Interfaces can be declared in a very similar manner to classes. All members of
-an interface must be declared as abstract.
+an interface are implicitly abstract.
 
 ````javascript
     var MyType = Interface(
     {
-        'abstract public foo': []
+        'public foo': []
     });
 ````
 

lib/interface.js

@@ -210,34 +210,22 @@ var extend = ( function( extending )
         var new_interface = createInterface( iname );
 
         util.propParse( props, {
+            assumeAbstract: true,
+
             property: function()
             {
-                throw TypeError(
-                    "Property not permitted within definition of " +
-                        "Interface '" + iname + "' (did you forget the " +
-                        "'abstract' keyword?)"
-                );
+                // should never get to this point because of assumeAbstract
+                throw TypeError( 'Unexpected internal error' );
             },
 
             getset: function()
             {
-                throw TypeError(
-                    "Getters/setters are not permitter within definition " +
-                    "of Interface '" + iname + "'"
-                );
+                // should never get to this point because of assumeAbstract
+                throw TypeError( 'Unexpected internal error' );
             },
 
             method: function( name, value, is_abstract, keywords )
             {
-                if ( !is_abstract )
-                {
-                    throw TypeError(
-                        "Concrete method not permitted in declaration of " +
-                            "Interface '" + iname + "'; please declare as " +
-                            "abstract."
-                    );
-                }
-
                 // all members must be public
                 if ( keywords[ 'protected' ] || keywords[ 'private' ] )
                 {

lib/util.js

@@ -297,7 +297,7 @@ exports.propParse = function( data, options )
         name       = parse_data.name || prop;
         keywords   = parse_data.keywords || {};
 
-        if ( keywords['abstract'] )
+        if ( options.assumeAbstract || keywords['abstract'] )
         {
             if ( !( value instanceof Array ) )
             {

test/Interface/ExtendTest.js

@@ -38,11 +38,11 @@ common.testCase(
         this.baseTypes = [
             Interface.extend(
             {
-                'abstract method': [],
+                method: [],
             } ),
 
             Interface( {
-                'abstract method': [],
+                method: [],
             } )
         ];
 
@@ -113,14 +113,20 @@ common.testCase(
     },
 
 
-    'Abstract method declarations are permitted': function()
+    /**
+     * Declaring (but not defining) methods by specifying their arguments as
+     * arrays is supported, much like one would would declare an abstract method
+     * in a class. We do not require the abstract keyword, as it would be
+     * redundant.
+     */
+    'Method declarations (using arrays) are permitted': function()
     {
         this.assertDoesNotThrow(
             function()
             {
                 Interface.extend(
                 {
-                    'abstract method': [],
+                    method: [],
                 } );
             },
             TypeError,
@@ -200,7 +206,7 @@ common.testCase(
     {
         var SubType = Interface.extend( T,
         {
-            'abstract second': [],
+            second: [],
         } );
 
         this.assertOk(
@@ -247,7 +253,7 @@ common.testCase(
     {
         var SubType = T.extend(
         {
-            'abstract second': [],
+            second: [],
         } );
 
         this.assertOk(
@@ -319,7 +325,7 @@ common.testCase(
         {
             // am = access modifier
             var dfn = {};
-            dfn[ 'abstract ' + am + ' foo' ] = [];
+            dfn[ am + ' foo' ] = [];
 
             Interface( dfn );
         }, Error, "Interface members should not be able to be " + am );