DEV Community: Towry

Answer: How do I convert from a char array [char; N] to a string slice &str?

Towry — Sat, 20 Jul 2024 04:54:20 +0000

Jul 13 '16

You can't without some allocation, which means you will end up with a String.

let s2: String = s.iter().collect();

The problem is that strings in Rust are not collections of chars, they are UTF-8, which is an encoding without a fixed size per character.

For example, the array…

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Answer: What is "Orthogonality"?

Towry — Mon, 27 Dec 2021 14:58:01 +0000

answer re: What is "Orthogonality"?

Oct 6 '09

From Eric S. Raymond's "Art of UNIX programming"

Orthogonality is one of the most important properties that can help make even complex designs compact. In a purely orthogonal design, operations do not have side effects; each action (whether it's an API call, a macro invocation, or a language operation) changes…

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简单方法写高质量的代码

Towry — Sat, 25 Dec 2021 08:13:54 +0000

首先，要知道单元测试是怎么写的。

下面是一个要测试的函数：

function add(a: number; b: number;) {
   return a + b;
}

我们要写单元测试，保证这个函数是OK的：


describe('add', () => {
  it('should work', () => {
     expect(add(1, 2)).toBe(3);
     expect(add(4, 4)).toBe(8);
  })
})

如果我们给的测试用例都能通过，那么说明我们的方法是安全可用的。

所以，在你写模块，写函数的时候，如果你的模块，函数，能被很容易的单元测试，那么你写的模块，函数就是80%安全可用的，出现bug的几率很少的。

但是，假如我们把上面的函数改变下：

import { addByRemote } from './api.js';

async function add(a: number; b: number) {
  return await addByRemote(a, b);
}

现在这个函数可以很方便的被单元测试吗？答案是不能。因为它依赖了一个接口调用，这个依赖的实现逻辑复杂度是不能确定的，但是我们把它耦合到了我们的add方法里了，那么我们的add方法逻辑就包含了这个接口的逻辑。

我们的add只是个例子，里面的逻辑很简单，但是想像这是个很复杂的业务逻辑，我们要写单元测试，保证这个业务逻辑是OK的，但是因为这个接口调用，我们的业务逻辑变得更复杂更臃肿了。我们的业务逻辑只是依赖这个接口的结果，不想关心接口里面的逻辑的。你如果把这个接口的结果看成函数的参数，就很好理解了。

现在这个 add 函数无法进行单元测试的，因为我们很难模拟这个 http 接口请求，我们可以称这个接口请求为副作用。如果这样的副作用变得多了，那么这个函数变得更加不稳定，更加难于测试了。

那么怎么处理这样的情况呢？

方法1: 把接口的结果作为参数传入我们的函数。
方法2: 通过依赖注入的方式，将这个API注入进去。这样的好处是，我们在单元测试的时候，可以注入一个我们模拟的函数作为这个API。

结论：如果你写的函数，不能很容易的被单元测试，那么你就需要考虑你的函数里面的依赖关系了，否则你写的就是一个很不好的代码。

Answer: Why can't I assign one dereference of a reference of a reference to another when the outer lifetimes differ?

Towry — Mon, 13 Dec 2021 09:16:09 +0000

answer re: Why can't I assign one dereference of a reference of a reference to another when the outer lifetimes differ?

Apr 13 '20

You cannot dereference a &'b mut &'c mut u32 and get a &'c mut u32 because:

&mut references are not trivially copiable, so you can't copy the &'c mut u32; and
You cannot move out of a reference, so you also can't move the &'c mut u32 (which would…

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Answer: How dependency injection in Angular is useful since it doesn't solve anything apparently?

Towry — Thu, 22 Apr 2021 05:55:44 +0000

answer re: How dependency injection in Angular is useful since it doesn't solve anything apparently?

Sep 18 '18

First of all, it's a bad question for StackOverflow But it deserves the answer. So here is it.

If you don't use Dependency Injection

The main difference is that if you don't use DI (dependency injection) then your code MUST know how to create all of its dependencies. You may…

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Answer: Angular2 How can I override provider

Towry — Sat, 20 Feb 2021 02:59:51 +0000

answer re: Angular2 How can I override provider

Jan 17 '17

https://angular.io/guide/ngmodule-faq#what-if-two-modules-provide-the-same-service

What if two modules provide the same service? When two imported modules, loaded at the same time, list a provider with the same token, the second module's provider "wins". That's because both providers are added to the same injector.

When Angular looks to inject a service for that token…

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Answer: What is lexical scope?

Towry — Fri, 06 Nov 2020 09:47:10 +0000

answer re: What is lexical scope?

Jun 26 '09

704

I understand them through examples. :)

First, lexical scope (also called static scope), in C-like syntax:

void fun()
{
    int x = 5;

    void fun2()
    {
        printf("%d", x);
    }
}

Every inner level can access its outer levels.

There is another way, called dynamic scope used by the first…

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Answer: What does “dereferencing” a pointer mean?

Towry — Thu, 20 Aug 2020 08:47:50 +0000

answer re: What does "dereferencing" a pointer mean?

Feb 10 '11

740

Reviewing the basic terminology

It's usually good enough - unless you're programming assembly - to envisage a pointer containing a numeric memory address, with 1 referring to the second byte in the process's memory, 2 the third, 3 the fourth and so on....

What happened to 0 and the first…

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Answer: What is the difference between casting and coercing?

Towry — Thu, 20 Aug 2020 03:22:37 +0000

answer re: What is the difference between casting and coercing?

Jan 13 '12

111

Type Conversion:

The word conversion refers to either implicitly or explicitly changing a value from one data type to another, e.g. a 16-bit integer to a 32-bit integer.

The word coercion is used to denote an implicit conversion.

The word cast typically refers to an explicit type conversion (as…

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Answer: could be instantiated with a different subtype of constraint 'object'

Towry — Thu, 28 May 2020 10:48:39 +0000

answer re: could be instantiated with a different subtype of constraint 'object'

Dec 16 '19

Complementing @fetzz great answer.

SHORT ANSWER

TLDR; There are two common causes for this kind of error message. You are doing the first one (see bellow). Along the text I explain in rich details what this error message want to convey.

CAUSE 1: In typscript, a generic type parameter is…

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Answer: Finding the point of a slope change as a free parameter- Python

Towry — Sun, 15 Sep 2019 05:54:52 +0000

answer re: Finding the point of a slope change as a free parameter- Python

Jul 12 '17

Here is a plot of your data:

You need to find two slopes (== taking two derivatives). First, find the slope between every two points (using numpy):

import numpy as np 
x = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10],dtype=np.float)
y = np.array([1, 2, 3, 4,

…

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Hello World

Towry — Thu, 31 Aug 2017 01:11:27 +0000

console.log("hello world");