Improve exercises

Author: gvergnaud

08-using-everything/exercises.ts

@@ -6,7 +6,7 @@
 // This an ESLint issue, not a typescript issue, you can trust other errors :)
 type TriggerESLintIssue = `${"a"}`;
 
-import { Equal, Expect, TODO } from "../helpers";
+import { Compute, Equal, Expect, TODO } from "../helpers";
 
 /**
  * 1. Implement a `ExtractUrlParamNames<url>` generic
@@ -36,10 +36,12 @@ namespace two {
   type ExtractUrlParams<url> = TODO;
 
   type res1 = ExtractUrlParams<"/user/:username">;
-  type test1 = Expect<Equal<res1, { username: string }>>;
+  type test1 = Expect<Equal<Compute<res1>, { username: string }>>;
 
   type res2 = ExtractUrlParams<"/user/:username/post/:postId">;
-  type test2 = Expect<Equal<res2, { username: string; postId: string }>>;
+  type test2 = Expect<
+    Equal<Compute<res2>, { username: string; postId: string }>
+  >;
 }
 
 namespace bonus {
@@ -54,10 +56,20 @@ namespace bonus {
     type ExtractUrlParams<url> = TODO;
 
     type res3 = ExtractUrlParams<"/dashboard(/:dashboardId)">;
-    type test3 = Expect<Equal<res3, { dashboardId?: string }>>;
+    type test3 = Expect<Equal<Compute<res3>, { dashboardId?: string }>>;
 
     type res4 = ExtractUrlParams<"org/:orgId/dashboard(/:dashboardId)">;
-    type test4 = Expect<Equal<res4, { orgId: string; dashboardId?: string }>>;
+    type test4 = Expect<
+      Equal<Compute<res4>, { orgId: string; dashboardId?: string }>
+    >;
+    type res5 =
+      ExtractUrlParams<"org/:orgId/dashboard(/:dashboardId/widgets/:widgetId)">;
+    type test5 = Expect<
+      Equal<
+        Compute<res5>,
+        { orgId: string; dashboardId?: string; widgetId?: string }
+      >
+    >;
   }
 
   /**

08-using-everything/solution.ts

@@ -6,7 +6,7 @@
 // This an ESLint issue, not a typescript issue, you can trust other errors :)
 type TriggerESLintIssue = `${"a"}`;
 
-import { Equal, Expect } from "../helpers";
+import { Compute, Equal, Expect } from "../helpers";
 
 /**
  * 1. Implement a `ExtractUrlParamNames<url>` generic
@@ -52,10 +52,12 @@ namespace two {
       : {};
 
   type res1 = ExtractUrlParams<"/user/:username">;
-  type test1 = Expect<Equal<res1, { username: string }>>;
+  type test1 = Expect<Equal<Compute<res1>, { username: string }>>;
 
   type res2 = ExtractUrlParams<"/user/:username/post/:postId">;
-  type test2 = Expect<Equal<res2, { username: string } & { postId: string }>>;
+  type test2 = Expect<
+    Equal<Compute<res2>, { username: string; postId: string }>
+  >;
 }
 
 namespace bonus {
@@ -76,11 +78,20 @@ namespace bonus {
         : {};
 
     type res3 = ExtractUrlParams<"/dashboard(/:dashboardId)">;
-    type test3 = Expect<Equal<res3, { dashboardId?: string }>>;
+    type test3 = Expect<Equal<Compute<res3>, { dashboardId?: string }>>;
 
     type res4 = ExtractUrlParams<"org/:orgId/dashboard(/:dashboardId)">;
     type test4 = Expect<
-      Equal<res4, { orgId: string } & { dashboardId?: string }>
+      Equal<Compute<res4>, { orgId: string; dashboardId?: string }>
+    >;
+
+    type res5 =
+      ExtractUrlParams<"org/:orgId/dashboard(/:dashboardId/widgets/:widgetId)">;
+    type test5 = Expect<
+      Equal<
+        Compute<res5>,
+        { orgId: string; dashboardId?: string; widgetId?: string }
+      >
     >;
   }
 

helpers.ts

@@ -15,7 +15,13 @@ export type Expect<T extends true> = T;
 export type Tuple = [any, ...any[]];
 
 const TODO = Symbol("TODO");
-export type TODO = any & typeof TODO;
+export type TODO = typeof TODO;
 
-// { a: string } & { b: string } -> { a: string, b: string }
+/**
+ * Compute is a helper converting intersections of objects into
+ * flat, plain object types.
+ *
+ * @example
+ * Compute<{ a: string } & { b: string }> -> { a: string, b: string }
+ */
 export type Compute<obj> = { [k in keyof obj]: obj[k] } & unknown;