Allow interfaces in GraphQLObjectType to be a thunk

Author: schrockn-zz

src/type/__tests__/definition.js

@@ -159,6 +159,26 @@ describe('Type System: Example', () => {
     expect(schema.getTypeMap().SomeSubtype).to.equal(SomeSubtype);
   });
 
+  it('includes interfaces\' thunk subtypes in the type map', () => {
+    var SomeInterface = new GraphQLInterfaceType({
+      name: 'SomeInterface',
+      fields: {}
+    });
+
+    var SomeSubtype = new GraphQLObjectType({
+      name: 'SomeSubtype',
+      fields: {},
+      interfaces: () => [SomeInterface]
+    });
+
+    var schema = new GraphQLSchema({
+      query: SomeInterface
+    });
+
+    expect(schema.getTypeMap().SomeSubtype).to.equal(SomeSubtype);
+  });
+
+
   it('stringifies simple types', () => {
 
     expect('' + GraphQLInt).to.equal('Int');

src/type/definition.js

@@ -252,6 +252,7 @@ export class GraphQLObjectType {
 
   _typeConfig: GraphQLObjectTypeConfig;
   _fields: GraphQLFieldDefinitionMap;
+  _interfaces: Array<GraphQLInterfaceType>;
 
   constructor(config: GraphQLObjectTypeConfig) {
     invariant(config.name, 'Type must be named.');
@@ -267,7 +268,8 @@ export class GraphQLObjectType {
   }
 
   getInterfaces(): Array<GraphQLInterfaceType> {
-    return this._typeConfig.interfaces || [];
+    return this._interfaces ||
+      (this._interfaces = defineInterfaces(this._typeConfig.interfaces || []));
   }
 
   isTypeOf(value: any): ?boolean {
@@ -282,10 +284,18 @@ export class GraphQLObjectType {
   }
 }
 
+function resolveMaybeThunk<T>(thingOrThunk: T | () => T): T {
+  return typeof thingOrThunk === 'function' ? thingOrThunk() : thingOrThunk;
+}
+
+function defineInterfaces(interfacesOrThunk): Array<GraphQLInterfaceType> {
+  return resolveMaybeThunk(interfacesOrThunk);
+}
+
 function defineFieldMap(
   fields: GraphQLFieldConfigMap
 ): GraphQLFieldDefinitionMap {
-  var fieldMap: any = typeof fields === 'function' ? fields() : fields;
+  var fieldMap: any = resolveMaybeThunk(fields);
   Object.keys(fieldMap).forEach(fieldName => {
     var field = fieldMap[fieldName];
     field.name = fieldName;