SafeMath类.如何创建可链计算?

Question

我很难在网上找到搜索这个的关键字。

我创建了一个具有安全数学函数的类。每个函数都有2个参数，在被一个断言求值后，它返回结果。

的例子:

class SafeMath {
static add(x: number, y: number) {
let z: number = x + y;
assert(z >= x, 'ds-math-add-overflow');
return z;
}
static sub(x: number, y: number) {
let z: number = x - y;
assert(z <= x, 'ds-math-sub-underflow');
return z;
}
static mul(x: number, y: number) {
let z: number = x * y;
assert(y == 0 || z / y == x, 'ds-math-mul-overflow');
return z;
}
static div(x: number, y: number) {
let z: number = x / y;
assert(x > 0 || y > 0, 'ds-math-div-by-zero');
return z;
}
}
console.log(SafeMath.add(2,2)); // 4
console.log(SafeMath.sub(2,2)); // 0
console.log(SafeMath.mul(2,2)); // 4
console.log(SafeMath.div(2,2)); // 1

我的目标是让这些函数像这样工作，例如:

let balance0: number = 1;
let balance1: number = 1;
let amount0In: number = 10;
let amount1In: number = 10;
let balance0Adjusted: number = balance0.mul(1000).sub(amount0In.mul(3));
let balance1Adjusted: number = balance1.mul(1000).sub(amount1In.mul(3));

…函数将取y，并使用之前的数字作为x。

Answer 1

您可以为它制作一些包装器:

if (!Number.prototype.mul)  // check that the mul method does not already exist 
{
Number.prototype.mul = function(n){ return this * n }
}

if (!Number.prototype.add)
{
Number.prototype.add = function(n){ return this + n }
}


let val = 5
let doubleValPlus500 = val.mul(2).add(500)
console.log( doubleValPlus500 )

Answer 2

您可以修改Number.prototype以添加函数，以便将这些操作链接起来。使用string属性键这样做通常被认为是一个不好的做法(参见为什么扩展本机对象是一个不好的做法?)。您可以使用唯一的符号属性键而不是字符串属性键来避免名称冲突等。

这是一个安全地"扩展"的示例模块。Number.prototype中添加了一个使用唯一符号的乘法函数，并在TypeScriptNumber接口中添加了新的函数签名:

mul.ts

const mul = Symbol("multiply");
function value(this: number, n: number) {
return this * n;
}
declare global {
interface Number {
[mul]: typeof value;
}
}
Object.defineProperty(Number.prototype, mul, { value });
export default mul;

像上面那样定义了一个用于减法、加法、除法等的模块之后，你就可以导入这些模块，并使用它们导出的唯一符号进行连锁操作:

import mul from "./mul.ts";
import sub from "./sub.ts";
const balance = 1;
const amountIn = 10;
const balanceAdjusted = balance[mul](1000)[sub](amountIn[mul](3));
console.log(balanceAdjusted);

970

使这些数学运算链化的一个好处是，当你处理空值时，你可以将它们与可选的链化操作符组合在一起，这有时会派上用场。

---

同样可以在不使用符号的情况下完成，但它不安全，因为未来的JavaScript版本可能会为mul定义自己的Number方法，等等:

mul.ts

function value(this: number, n: number) {
return this * n;
}
declare global {
interface Number {
mul: typeof value;
}
}
Object.defineProperty(Number.prototype, "mul", { value });
export {}; // you have to import or export something to make it a module

import "./mul.ts";
import "./sub.ts";
const balance = 1;
const amountIn = 10;
const balanceAdjusted = balance.mul(1000).sub(amountIn.mul(3));
console.log(balanceAdjusted);

970

---

单独导入所有这些模块可能不是很方便，所以您也可以创建一个单独的模块来组合所有其他模块:

math.ts

export { default as mul } from "./mul.ts";
export { default as sub } from "./sub.ts";
/* and so forth */

然后你可以导入它并选择你想要使用的:

import { mul, sub } from "./math.ts";
const balance = 1;
const amountIn = 10;
const balanceAdjusted = balance[mul](1000)[sub](amountIn[mul](3));
console.log(balanceAdjusted);

Answer 3

号码。基于原型的示例

import { assert } from "https://deno.land/std@0.102.0/testing/asserts.ts";
declare global {
/*
Augument global Number.prototype with the following custom functions
Warning - While this may look like a clean approach, it is considered 
unsafe due to javascript possibly choosing to natively implement these
exact function names in the near future. To avoid this, choose unique
function names.
*/
interface Number {
add(n: number): number;
sub(n: number): number;
mul(n: number): number;
div(n: number): number;
pow(n: number): number;
sqrt(): number;
print(): number;
}
}
Number.prototype.add = function(this:number, n:number) {
assert((this + n) >= this, 'ds-math-add-overflow');
return this + n;
}
Number.prototype.sub = function(this:number, n:number) {
assert((this - n) <= this, 'ds-math-sub-underflow');
return this - n;
}
Number.prototype.mul = function(this:number, n:number) {
assert(n == 0 || (this * n) / n == this, 'ds-math-mul-overflow');
return this * n;
}
Number.prototype.div = function(this:number, n:number) {
assert(this > 0 || n > 0, 'ds-math-div-by-zero');
return this / n;
}
Number.prototype.pow = function(this:number, n:number) {
assert(this > 0 && n >= 2, 'ds-math-exp-to-zero');
return this ** n;
}
// babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
Number.prototype.sqrt = function(this:number) {
assert(this > 0, 'ds-math-sqrt-of-zero');
let x: number = 0;
let y: number = this;
let z: number = 0;
if (y > 3) {
z = y;
x = y / 2 + 1;
while (x < z) {
z = x;
x = (y / x + x) / 2;
}
} else if (y != 0) {
z = 1;
}
return z;
}
Number.prototype.print = function(this:number) {
console.log('=', this);
return this;
}
// Here it is in action:
let balance = 0;
balance.add(10).print().sub(1).print().mul(2).print().div(3).print().pow(4).print().sqrt().print();

输出:

= 10
= 9
= 18
= 6
= 1296
= 36

基于类的示例

import { assert } from "https://deno.land/std@0.102.0/testing/asserts.ts";
class SafeMath {
private n: number;
constructor(start: number = 0) {
this.n = start;
}
public add(y: number) {
assert(this.n + y >= this.n, 'ds-math-add-overflow');
let z: number = this.n + y;
this.n = this.n + y;
return this;
}
public sub(y: number) {
assert(this.n - y <= this.n, 'ds-math-sub-underflow');
let z: number = this.n - y;
this.n = this.n - y;
return this;
}
public mul(y: number) {
assert(y == 0 || (this.n * y) / y == this.n, 'ds-math-mul-overflow');
let z: number = this.n * y;
this.n = this.n * y;
return this;
}
public div(y: number) {
assert(this.n > 0 || y > 0, 'ds-math-div-by-zero');
let z: number = this.n / y;
this.n = this.n / y;
return this;
}
public pow(y: number) {
assert(this.n > 0 && y >= 2, 'ds-math-exp-to-zero');
let z: number = this.n ** y;
this.n = this.n ** y;
return this;
}
// babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
public sqrt() {
assert(this.n > 0, 'ds-math-sqrt-of-zero');
let x: number = 0;
let y: number = this.n;
let z: number = 0;
if (y > 3) {
z = y;
this.n = z;
x = y / 2 + 1;
while (x < z) {
z = x;
this.n = z
x = (y / x + x) / 2;
}
} else if (y != 0) {
z = 1;
this.n = z
}
return this;
}
public print() {
console.log('=', this.n);
return this;
}
}
// Here it is in action:
new SafeMath(0).add(10).print().sub(1).print().mul(2).print().div(3).print().pow(4).print().sqrt().print();

输出:

= 10
= 9
= 18
= 6
= 1296
= 36