Added a note about experimental executor in the changelog

CHANGELOG.md

@@ -3,11 +3,18 @@
 This release brings several breaking changes. Please refer to [UPGRADE](UPGRADE.md) document for details.
 
 New features and notable changes:
+- New experimental executor with improved performance (#314).<br>
+It is a one-line switch: `GraphQL::useExperimentalExecutor()`.<br>
+<br> 
+**Please try it and post your feedback at https://github.com/webonyx/graphql-php/issues/397**
+(as it may become the default one in future)
+<br>
+<br> 
 - Spec compliance: error category, debug information and extensions are displayed under `extensions` key 
 - `AbstractValidationRule` renamed to `ValidationRule` (NS `GraphQL\Validator\Rules`)
 - `AbstractQuerySecurity` renamed to `QuerySecurityRule` (NS `GraphQL\Validator\Rules`)
 - `FindBreakingChanges` renamed to `BreakingChangesFinder` (NS `GraphQL\Utils`)
-- Added ability to override standard types via `GraphQL::overrideStandardTypes(array $types)`
+- Added ability to override standard types via `GraphQL::overrideStandardTypes(array $types)` (#401)
 
 #### v0.12.5
 - Execution performance optimization for lists

src/GraphQL.php

@@ -10,6 +10,8 @@ use GraphQL\Executor\Executor;
 use GraphQL\Executor\Promise\Adapter\SyncPromiseAdapter;
 use GraphQL\Executor\Promise\Promise;
 use GraphQL\Executor\Promise\PromiseAdapter;
+use GraphQL\Executor\ReferenceExecutor;
+use GraphQL\Experimental\Executor\CoroutineExecutor;
 use GraphQL\Language\AST\DocumentNode;
 use GraphQL\Language\Parser;
 use GraphQL\Language\Source;
@@ -319,6 +321,22 @@ class GraphQL
         Executor::setPromiseAdapter($promiseAdapter);
     }
 
+    /**
+     * Experimental: Switch to the new executor
+     */
+    public static function useExperimentalExecutor()
+    {
+        Executor::setImplementationFactory([CoroutineExecutor::class, 'create']);
+    }
+
+    /**
+     * Experimental: Switch back to the default executor
+     */
+    public static function useReferenceExecutor()
+    {
+        Executor::setImplementationFactory([ReferenceExecutor::class, 'create']);
+    }
+
     /**
      * Returns directives defined in GraphQL spec
      *