Adding outtput delegation API

Sources/GraphZahl/Resolution/OutputResolvable/DelegatedOutputResolvable.swift

@@ -0,0 +1,52 @@
+
+import Foundation
+import ContextKit
+import NIO
+import GraphQL
+
+protocol DelegatedOutputResolvable: OutputResolvable {
+    associatedtype Output: OutputResolvable
+
+    func resolve(source: Any,
+                 arguments: [String : Map],
+                 context: MutableContext,
+                 eventLoop: EventLoopGroup) throws -> Output
+}
+
+extension DelegatedOutputResolvable {
+
+    /**
+     - Warning: default implementation from `GraphZahl`. Do not override unless you know exactly what you are doing.
+     */
+    public static var additionalArguments: [String : InputResolvable.Type] {
+        return Output.additionalArguments
+    }
+
+    /**
+     - Warning: default implementation from `GraphZahl`. Do not override unless you know exactly what you are doing.
+     */
+    public static func reference(using context: inout Resolution.Context) throws -> GraphQLOutputType {
+        return try context.reference(for: Output.self)
+    }
+
+    /**
+     - Warning: default implementation from `GraphZahl`. Do not override unless you know exactly what you are doing.
+     */
+    public static func resolve(using context: inout Resolution.Context) throws -> GraphQLOutputType {
+        return try context.resolve(type: Output.self)
+    }
+
+    /**
+     - Warning: default implementation from `GraphZahl`. Do not override unless you know exactly what you are doing.
+     */
+    public func resolve(source: Any,
+                        arguments: [String : Map],
+                        context: MutableContext,
+                        eventLoop: EventLoopGroup) throws -> EventLoopFuture<Any?> {
+
+        return try resolve(source: source, arguments: arguments, context: context, eventLoop: eventLoop)
+            .resolve(source: source, arguments: arguments, context: context, eventLoop: eventLoop)
+    }
+
+
+}

Sources/GraphZahlTests/SchemaResolutionTests.swift

@@ -38,6 +38,28 @@ class SchemaResolutionTests: XCTestCase {
         XCTAssertEqual(expectedData, result.data)
     }
 
+    func testDelegatedOutputs() throws {
+        struct SomeInt: DelegatedOutputResolvable {
+            let int: Int
+
+            func resolve(source: Any, arguments: [String : Map], context: MutableContext, eventLoop: EventLoopGroup) throws -> some OutputResolvable {
+                return int
+            }
+        }
+
+        var context = Resolution.Context.empty(viewerContextType: Int.self, viewerContext: 42)
+        let output = try SomeInt.resolve(using: &context)
+        guard let nonNull = output as? GraphQLNonNull else {
+            XCTFail("outptut of some int is nullable")
+            return
+        }
+        guard let scalar = nonNull.ofType as? GraphQLScalarType else {
+            XCTFail("outptut of some int is not a scalar")
+            return
+        }
+        XCTAssertEqual(scalar, GraphQLInt)
+    }
+
     func testKeypaths() throws {
         let query = """
         {