From 8f91ed71aa622233725d56da98e5ca051e08321e Mon Sep 17 00:00:00 2001
From: Matt Pocock <mattpocockvoice@gmail.com>
Date: Wed, 13 Sep 2023 10:17:13 +0100
Subject: [PATCH] 2023-09-13T09:17:13.105Z

---
 .../helpers.d.ts                                | 17 +++++++++++++++++
 .../package.json                                |  8 ++++++++
 .../src/index.ts                                |  5 +++++
 .../tsconfig.json                               | 12 ++++++++++++
 .../helpers.d.ts                                | 17 +++++++++++++++++
 .../package.json                                |  8 ++++++++
 .../src/index.ts                                |  5 +++++
 .../tsconfig.json                               | 13 +++++++++++++
 .../192-tsconfig-bases.explainer.ts             |  2 ++
 9 files changed, 87 insertions(+)
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/helpers.d.ts
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/package.json
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/src/index.ts
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/tsconfig.json
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/helpers.d.ts
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/package.json
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/src/index.ts
 create mode 100644 src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/tsconfig.json

diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/helpers.d.ts b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/helpers.d.ts
new file mode 100644
index 0000000..3ae28b9
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/helpers.d.ts
@@ -0,0 +1,17 @@
+type Expect<T extends true> = T;
+type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y
+  ? 1
+  : 2
+  ? true
+  : false;
+
+/**
+ * Checks that Y is assignable to X.
+ *
+ * For instance, `Extends<string, 'a'>` is true. This is because
+ * 'a' can be passed to a function which expects a string.
+ *
+ * But `Extends<'a', string>` is false. This is because a string
+ * CANNOT be passed to a function which expects 'a'.
+ */
+type Extends<X, Y> = Y extends X ? true : false;
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/package.json b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/package.json
new file mode 100644
index 0000000..e11b297
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "exercise",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "dev": "tsc --watch"
+  }
+}
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/src/index.ts b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/src/index.ts
new file mode 100644
index 0000000..231da65
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/src/index.ts
@@ -0,0 +1,5 @@
+const array = [1, 2, 3];
+
+const mightNotExist = array[3];
+
+type test = Expect<Equal<typeof mightNotExist, number | undefined>>;
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/tsconfig.json b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/tsconfig.json
new file mode 100644
index 0000000..4627a58
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.problem/tsconfig.json
@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "esModuleInterop": true,
+    "noEmit": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "isolatedModules": true,
+  },
+}
\ No newline at end of file
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/helpers.d.ts b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/helpers.d.ts
new file mode 100644
index 0000000..3ae28b9
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/helpers.d.ts
@@ -0,0 +1,17 @@
+type Expect<T extends true> = T;
+type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y
+  ? 1
+  : 2
+  ? true
+  : false;
+
+/**
+ * Checks that Y is assignable to X.
+ *
+ * For instance, `Extends<string, 'a'>` is true. This is because
+ * 'a' can be passed to a function which expects a string.
+ *
+ * But `Extends<'a', string>` is false. This is because a string
+ * CANNOT be passed to a function which expects 'a'.
+ */
+type Extends<X, Y> = Y extends X ? true : false;
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/package.json b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/package.json
new file mode 100644
index 0000000..e11b297
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "exercise",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "dev": "tsc --watch"
+  }
+}
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/src/index.ts b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/src/index.ts
new file mode 100644
index 0000000..231da65
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/src/index.ts
@@ -0,0 +1,5 @@
+const array = [1, 2, 3];
+
+const mightNotExist = array[3];
+
+type test = Expect<Equal<typeof mightNotExist, number | undefined>>;
diff --git a/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/tsconfig.json b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/tsconfig.json
new file mode 100644
index 0000000..dfb60b4
--- /dev/null
+++ b/src/080-configuring-typescript/191-no-unchecked-indexed-access.solution/tsconfig.json
@@ -0,0 +1,13 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "esModuleInterop": true,
+    "noEmit": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "isolatedModules": true,
+    "noUncheckedIndexedAccess": true
+  },
+}
\ No newline at end of file
diff --git a/src/080-configuring-typescript/192-tsconfig-bases.explainer.ts b/src/080-configuring-typescript/192-tsconfig-bases.explainer.ts
index ec728ab..e638fb6 100644
--- a/src/080-configuring-typescript/192-tsconfig-bases.explainer.ts
+++ b/src/080-configuring-typescript/192-tsconfig-bases.explainer.ts
@@ -1 +1,3 @@
 // https://github.com/tsconfig/bases
+
+// Note that strictest is not what I recommend