Create ob1 package

Reviewed By: cpojer

Differential Revision: D15972397

fbshipit-source-id: 589cb663775c3560705c501a37c6be4559238015

packages/ob1/.npmignore

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+BUCK
+**/__mocks__/**
+**/__tests__/**
+build
+src.real
+yarn.lock

packages/ob1/README.md

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+# ob1
+
+A small library for working with 0- and 1-based offsets in a type-checked way.

packages/ob1/package.json

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+{
+  "name": "ob1",
+  "version": "0.54.1",
+  "description": "A small library for working with 0- and 1-based offsets in a type-checked way.",
+  "main": "src/ob1.js",
+  "repository": {
+    "type": "git",
+    "url": "git@github.com:facebook/metro.git"
+  },
+  "scripts": {
+    "prepare-release": "test -d build && rm -rf src.real && mv src src.real && mv build src",
+    "cleanup-release": "test ! -e build && mv src build && mv src.real src"
+  },
+  "keywords": [
+    "metro"
+  ],
+  "license": "MIT",
+  "dependencies": {}
+}

packages/ob1/src/__flowtests__/ob1-flowtest.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @emails oncall+metro_bundler
+ */
+
+'use strict';
+
+const {add, get0, get1, add1, sub1, sub, neg, add0, inc} = require('../ob1');
+
+import type {Number0, Number1} from '../ob1';
+const FORTY_TWO_0 = add0(42);
+const FORTY_TWO_1 = add1(42);
+
+module.exports = {
+  testSafeOps() {
+    (add(FORTY_TWO_0, FORTY_TWO_0): Number0);
+    (add(FORTY_TWO_0, FORTY_TWO_1): Number1);
+    (add(FORTY_TWO_1, FORTY_TWO_0): Number1);
+    (sub(FORTY_TWO_1, FORTY_TWO_1): Number0);
+    (add(FORTY_TWO_0, 9000): Number0);
+    (add(FORTY_TWO_0, 9000): Number0);
+    (add(FORTY_TWO_1, 9000): Number1);
+    (sub(FORTY_TWO_1, 9000): Number1);
+    (get0(FORTY_TWO_0): number);
+    (get1(FORTY_TWO_1): number);
+    (neg(FORTY_TWO_0): Number0);
+    (add1(FORTY_TWO_0): Number1);
+    (sub1(FORTY_TWO_1): Number0);
+    (inc(FORTY_TWO_0): Number0);
+    (inc(FORTY_TWO_1): Number1);
+  },
+  testUnsafeOps() {
+    // $FlowExpectedError - adding two 1-based offsets.
+    add(FORTY_TWO_1, FORTY_TWO_1);
+
+    // $FlowExpectedError - subtracting 1-based offset from 0-based offset.
+    sub(FORTY_TWO_0, FORTY_TWO_1);
+
+    // $FlowExpectedError - direct computations with offsets are disallowed.
+    FORTY_TWO_0 - 1;
+
+    // $FlowExpectedError - direct computations with offsets are disallowed.
+    FORTY_TWO_1 - 1;
+
+    // $FlowExpectedError - extracting a 1-based offset as a 0-based number
+    get0(FORTY_TWO_1);
+
+    // $FlowExpectedError - extracting a 0-based offset as a 1-based number
+    get1(FORTY_TWO_0);
+
+    // $FlowExpectedError - negating a 1-based offset
+    neg(FORTY_TWO_1);
+
+    // $FlowExpectedError - adding 1 to an offset that's already 1-based
+    add1(FORTY_TWO_1);
+
+    // $FlowExpectedError - subtracting 1 from an offset that's already 0-based
+    sub1(FORTY_TWO_0);
+
+    // $FlowExpectedError - extracting an arbitrary number as a 0-based number
+    get0(42);
+
+    // $FlowExpectedError - extracting an arbitrary number as a 1-based number
+    get1(42);
+  },
+};

packages/ob1/src/__tests__/ob1-test.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @emails oncall+metro_bundler
+ */
+
+'use strict';
+
+const {add, get0, get1, add1, sub1, sub, neg, add0, inc} = require('../ob1');
+
+const FORTY_TWO_0 = add0(42);
+const FORTY_TWO_1 = add1(41);
+
+describe('ob1', () => {
+  test('add', () => {
+    expect(get0(add(FORTY_TWO_0, 3))).toBe(45);
+    expect(get1(add(FORTY_TWO_1, 3))).toBe(45);
+  });
+
+  test('sub', () => {
+    expect(get0(sub(FORTY_TWO_0, 3))).toBe(39);
+    expect(get1(sub(FORTY_TWO_1, 3))).toBe(39);
+  });
+
+  test('neg', () => {
+    expect(get0(neg(FORTY_TWO_0))).toBe(-42);
+  });
+
+  test('inc', () => {
+    expect(get0(inc(FORTY_TWO_0))).toBe(43);
+    expect(get1(inc(FORTY_TWO_1))).toBe(43);
+  });
+
+  test('add1', () => {
+    expect(get1(add1(FORTY_TWO_0))).toBe(43);
+  });
+
+  test('sub1', () => {
+    expect(get0(sub1(FORTY_TWO_1))).toBe(41);
+  });
+});

packages/ob1/src/ob1.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+'use strict';
+
+/* eslint-disable no-redeclare */
+
+// A type representing 0-based offsets.
+export opaque type Number0 = number;
+// A type representing 1-based offsets.
+export opaque type Number1 = number;
+
+// Add two offsets or numbers.
+declare function add(a: Number1, b: number): Number1;
+declare function add(a: number, b: Number1): Number1;
+declare function add(a: Number0, b: number): Number0;
+declare function add(a: number, b: Number0): Number0;
+declare function add(a: Number1, b: Number0): Number1;
+declare function add(a: Number0, b: Number1): Number1;
+declare function add(a: Number0, b: Number0): Number0;
+
+function add(a, b) {
+  return a + b;
+}
+
+// Subtract a number or 0-based offset from a 1/0-based offset.
+declare function sub(a: Number1, b: number): Number1;
+declare function sub(a: Number0, b: number): Number0;
+declare function sub(a: number, b: Number0): Number0;
+declare function sub(a: Number0, b: number): Number0;
+declare function sub(a: Number1, b: Number0): Number1;
+declare function sub(a: Number0, b: Number0): Number0;
+declare function sub(a: Number1, b: Number1): Number0;
+
+function sub(a, b) {
+  return a - b;
+}
+
+// Get the underlying number of a 0-based offset, casting away the opaque type.
+declare function get0(x: Number0): number;
+declare function get0(x: void | null): void | null;
+function get0(x) {
+  return x;
+}
+
+// Get the underlying number of a 1-based offset, casting away the opaque type.
+declare function get1(x: Number1): number;
+declare function get1(x: void | null): void | null;
+function get1(x) {
+  return x;
+}
+
+// Add 1 to a 0-based offset, thus converting it to 1-based.
+function add1(x: Number0 | number): Number1 {
+  return x + 1;
+}
+
+// Subtract 1 from a 1-based offset, thus converting it to 0-based.
+function sub1(x: Number1): Number0 {
+  return x - 1;
+}
+
+// Negate a 0-based offset.
+function neg(x: Number0): Number0 {
+  return -x;
+}
+
+// Cast a number to a 0-based offset.
+function add0(x: number): Number0 {
+  return x;
+}
+
+// Increment a 0-based offset.
+declare function inc(a: Number0): Number0;
+// Increment a 1-based offset.
+declare function inc(a: Number1): Number1;
+
+function inc(x) {
+  return x + 1;
+}
+
+module.exports = {add, get0, get1, add1, sub1, sub, neg, add0, inc};