DanielRosenwasser

[[Early thoughts around conditional types]]

Conditional Types

• Currently have T extends Foo as a type operator that returns true or false.
  • Seems very strange as to what that actually means:

    declare function foo<T>(x: T, y: T extends string): void;

  • This function takes an x, and if x is a string, y must be true or otherwise false.

DanielRosenwasser

import ts = require("typescript");

function makeFactorialFunction() {
    const functionName = ts.createIdentifier("factorial");
    const paramName = ts.createIdentifier("n");
    const parameter = ts.createParameter(
        /*decorators*/ undefined,
        /*modifiers*/ undefined,
        /*dotDotDotToken*/ undefined,
        paramName);

DanielRosenwasser

declare function ava(              run: ava.ContextualTest): void;
declare function ava(name: string, run: ava.ContextualTest): void;
declare function ava(              run: ava.Macros<ava.ContextualTestContext>, ...args: Array<any>): void;
declare function ava(name: string, run: ava.Macros<ava.ContextualTestContext>, ...args: Array<any>): void;
declare namespace ava {
  /**
   * Misc Setup Types
   */
  export type PromiseLike<R> = {
    then<U>(

DanielRosenwasser

// Type definitions for axe-core 2.0.5
// Project: https://github.com/dequelabs/axe-core
// Definitions by: Marcy Sutton <https://github.com/marcysutton>
// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped

declare const enum Tags {"wcag2a", "wcag2aa", "section508", "best-practice"}

declare const enum Reporter {"v1", "v2"}

interface ElementContext {

DanielRosenwasser

Motivation

Originally we used contextual types to decide when to infer a string literal type. If a string literal had a contextual type, we'd create a literal type for the string. That was the only change.

We ran into two basic problems:

1. When you want to infer a string literal type for a variable, you always have to write a type annotation.

DanielRosenwasser

diff --git a/src/services/services.ts b/src/services/services.ts
index a9dda54..8f90284 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -12,7 +12,7 @@
 
 namespace ts {
     /** The version of the language service API */
-    export let servicesVersion = "0.4"
+    export const servicesVersion = "0.4";