selfOR_html, body {overflow-x: initial !important;}html { font-size: 14px; }
body { margin: 0px; padding: 0px; height: auto; bottom: 0px; top: 0px; left: 0px; right: 0px; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 1rem; line-height: 1.42857143; color: rgb(51, 51, 51); background-color: rgb(255, 255, 255); overflow-x: hidden; }
a:active, a:hover { outline: 0px; }
::selection { background-color: rgb(181, 214, 252); text-shadow: none; background-position: initial initial; background-repeat: initial initial; }
#write { margin: 0px auto; height: auto; width: inherit; word-break: normal; word-wrap: break-word; position: relative; white-space: pre-wrap; text-align: justify; padding-bottom: 70px; }
body.typora-export { padding-left: 30px; padding-right: 30px; }
.typora-export #write { margin: 0px auto; }
#write > p:first-child, #write > ul:first-child, #write > pre:first-child, #write > blockquote:first-child, #write > div:first-child { margin-top: 30px; }
img { max-width: 100%; }
input, button, select, textarea { color: inherit; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; }
input[type="checkbox"], input[type="radio"] { line-height: normal; padding: 0px; }
::before, ::after, * { box-sizing: border-box; }
#write p, #write h1, #write h2, #write h3, #write h4, #write h5, #write h6, #write div, #write pre { width: inherit; }
h1 { font-size: 2rem; }
p, .mathjax-block { display: block; -webkit-margin-before: 1rem; -webkit-margin-after: 1rem; -webkit-margin-start: 0px; -webkit-margin-end: 0px; }
.hidden { display: none; }
.md-blockmeta { color: rgb(204, 204, 204); font-weight: bold; font-style: italic; }
a { cursor: pointer; }
li span { min-width: 10px; }
#write input[type="checkbox"] { cursor: pointer; width: inherit; height: inherit; margin: 4px 0px 0px; }
tr { page-break-inside: avoid; page-break-after: auto; }
thead { display: table-header-group; }
table { border-collapse: collapse; border-spacing: 0px; width: 100%; overflow: auto; page-break-inside: auto; }
table.md-table td { min-width: 80px; }
.CodeMirror-placeholder { opacity: 0.3; }
.CodeMirror-code pre { padding: 0px; }
.CodeMirror-lines { padding: 0px; }
div.hr:focus { cursor: none; }
.md-fences, pre.md-fences { font-size: 0.9rem; display: block; page-break-inside: avoid; text-align: left; overflow: visible; white-space: pre; position: relative !important; }
.md-fences .CodeMirror.cm-s-default.CodeMirror-wrap { top: -1.6em; margin-bottom: -1.6em; }
.md-fences.mock-cm { white-space: pre-wrap; }
.footnotes { color: rgb(136, 136, 136); font-size: 0.9rem; padding-top: 1em; padding-bottom: 1em; }
.footnotes + .footnotes { margin-top: -1em; }
.md-reset { margin: 0px; padding: 0px; border: 0px; outline: 0px; vertical-align: top; background-color: transparent; text-decoration: none; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 1rem; text-shadow: none; float: none; position: static; width: auto; height: auto; white-space: nowrap; cursor: inherit; line-height: normal; font-weight: normal; text-align: left; box-sizing: content-box; direction: ltr; background-position: initial initial; background-repeat: initial initial; }
li div { padding-top: 0px; }
blockquote { margin: 1rem 0px; }
li p, li .mathjax-block { margin: 0.5rem 0px; }
li { margin: 0px; position: relative; }
blockquote > :last-child { margin-bottom: 0px; }
blockquote > :first-child { margin-top: 0px; }
.footnotes-area { color: rgb(136, 136, 136); margin-top: 0.714rem; padding-bottom: 0.143rem; }
@media print {
html, body { height: 100%; }
.typora-export * { -webkit-print-color-adjust: exact; }
}
.footnote-line { margin-top: 0.714em; font-size: 0.7em; }
a img, img a { cursor: pointer; }
#write pre.md-meta-block { font-size: 0.8rem; min-height: 2.86rem; white-space: pre; background-color: rgb(204, 204, 204); display: block; background-position: initial initial; background-repeat: initial initial; }
p > .md-image:only-child { display: inline-block; width: 100%; text-align: center; }
#write .MathJax_Display { margin: 0.8em 0px 0px; }
.mathjax-block { white-space: pre; padding-bottom: 0.65rem; overflow: hidden; width: 100%; }
p + .mathjax-block { margin-top: -1.143rem; }
.mathjax-block:not(:empty)::after { display: none; }
[contenteditable="true"]:active, [contenteditable="true"]:focus { outline: none; box-shadow: none; }
:focus { outline: none; box-shadow: rgb(79, 172, 249) 0px 0px 2px 3px, rgb(120, 174, 218) 0px 0px 2px inset; }
.task-list { list-style-type: none; }
.task-list-item { position: relative; padding-left: 1em; }
.task-list-item input { position: absolute; top: 0px; left: 0px; }
.math { font-size: 1rem; }
.md-toc { min-height: 3.58rem; position: relative; font-size: 0.9rem; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px; }
.md-toc-content { position: relative; margin-left: 0px; }
.md-toc::after, .md-toc-content::after { display: none; }
.md-toc-item { display: block; color: rgb(65, 131, 196); text-decoration: none; }
.md-toc-inner:hover { text-decoration: underline; }
.md-toc-inner { display: inline-block; cursor: pointer; }
.md-toc-h1 .md-toc-inner { margin-left: 0px; font-weight: bold; }
.md-toc-h2 .md-toc-inner { margin-left: 2em; }
.md-toc-h3 .md-toc-inner { margin-left: 4em; }
.md-toc-h4 .md-toc-inner { margin-left: 6em; }
.md-toc-h5 .md-toc-inner { margin-left: 8em; }
.md-toc-h6 .md-toc-inner { margin-left: 10em; }
.md-toc-h6 { margin-left: 12em; }
@media screen and (max-width: 48em) {
.md-toc-h3 .md-toc-inner { margin-left: 3.5em; }
.md-toc-h4 .md-toc-inner { margin-left: 5em; }
.md-toc-h5 .md-toc-inner { margin-left: 6.5em; }
.md-toc-h5 .md-toc-inner { margin-left: 8em; }
.md-toc-h6 { margin-left: 9.5em; }
}
a.md-toc-inner { color: inherit; font-size: inherit; font-style: inherit; font-weight: inherit; text-decoration: inherit; line-height: inherit; }
.footnote-line a:not(.reversefootnote) { color: inherit; }
.md-attr { display: none; }
.md-fn-count::after { content: '.'; }
.md-tag { opacity: 0.5; }
h1 .md-tag, h2 .md-tag, h3 .md-tag, h4 .md-tag, h5 .md-tag, h6 .md-tag { font-weight: initial; opacity: 0.35; }

html { font-size: 16px; }
html, body { background-color: rgb(243, 242, 238); font-family: 'PT Serif'; color: rgb(31, 9, 9); line-height: 1.5em; }
#write { max-width: 36em; }
ol, ul { list-style: none; }
blockquote, q { quotes: none; }
blockquote::before, blockquote::after, q::before, q::after { content: none; }
table { border-collapse: collapse; border-spacing: 0px; }
h1, h2, h3, h4, h5, h6 { font-weight: bold; }
h1 { font-size: 1.875em; line-height: 1.6em; margin-top: 2em; }
h2, h3 { font-size: 1.3125em; line-height: 1.15; margin-top: 2.285714em; margin-bottom: 1.15em; }
h3 { font-weight: normal; }
h4 { font-size: 1.125em; margin-top: 2.67em; }
h5, h6 { font-size: 1em; }
h1 { border-bottom-width: 1px; border-bottom-style: solid; margin-bottom: 1.875em; padding-bottom: 0.8125em; }
a { text-decoration: none; color: rgb(6, 85, 136); }
a:hover, a:active { text-decoration: underline; }
p, blockquote, pre.md-fences, .md-fences { margin-bottom: 1.5em; }
h1, h2, h3, h4, h5, h6 { margin-bottom: 1.5em; }
blockquote { font-style: italic; border-left-width: 5px; border-left-style: solid; margin-left: 2em; padding-left: 1em; }
ul, ol { margin: 0px 0px 1.5em 1.5em; }
ol li { list-style-type: decimal; list-style-position: outside; }
ul li { list-style-type: disc; list-style-position: outside; }
.md-meta, .md-before, .md-after { color: rgb(153, 153, 153); }
table { margin-bottom: 1.5em; font-size: 1em; }
thead th, tfoot th { padding: 0.25em 0.25em 0.25em 0.4em; text-transform: uppercase; }
th { text-align: left; }
td { vertical-align: top; padding: 0.25em 0.25em 0.25em 0.4em; }
code, pre.md-fences { background-color: rgb(218, 218, 218); padding-left: 1ch; padding-right: 1ch; }
pre.md-fences { margin-left: 2em; margin-bottom: 3em; }
pre, code, tt { font-size: 0.875em; line-height: 1.714285em; }
h1 { line-height: 1.3em; font-weight: normal; margin-bottom: 0.5em; }
p + ul, p + ol { margin-top: -1em; }
h3 + ul, h4 + ul, h5 + ul, h6 + ul, h3 + ol, h4 + ol, h5 + ol, h6 + ol { margin-top: 0.5em; }
li > ul, li > ol { margin-top: inherit; }
h2, h3 { margin-bottom: 0.75em; }
hr { border-style: none none solid; border-bottom-width: 1px; }
h1 { border-color: rgb(197, 197, 197); }
blockquote { border-color: rgb(186, 186, 186); color: rgb(101, 101, 101); }
thead.md-table-edit { background-color: transparent; }
thead { background-color: rgb(218, 218, 218); }
tr:nth-child(even) { background-color: rgb(232, 231, 231); background-position: initial initial; background-repeat: initial initial; }
hr { border-color: rgb(197, 197, 197); }
.task-list { padding-left: 1rem; }
.task-list-item { padding-left: 1.5rem; list-style-type: none; }
.task-list-item input::before { content: '√'; display: inline-block; width: 1.25rem; height: 1.5rem; vertical-align: middle; text-align: center; color: rgb(221, 221, 221); background-color: rgb(243, 242, 238); }
.task-list-item input:checked::before, .task-list-item input[checked]::before { color: inherit; }
#write pre.md-meta-block { min-height: 1.875rem; color: rgb(85, 85, 85); border: 0px; background-color: transparent; margin-left: 1em; margin-top: 1em; background-position: initial initial; background-repeat: initial initial; }
.md-image > .md-meta { color: rgb(155, 81, 70); }
.md-expand.md-image > .md-meta { background-color: rgba(255, 255, 255, 0.65098); }
.md-image > .md-meta { font-family: Menlo, 'Ubuntu Mono', Consolas, 'Courier New', 'Microsoft Yahei', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif; }
#write > h3.md-focus::before { left: -2.5rem; color: rgb(153, 153, 153); border-color: rgb(153, 153, 153); }
#write > h4.md-focus::before { left: -2.5rem; top: 0.25rem; color: rgb(153, 153, 153); border-color: rgb(153, 153, 153); }
#write > h5.md-focus::before { left: -2.5rem; color: rgb(153, 153, 153); border-color: rgb(153, 153, 153); }
#write > h6.md-focus::before { left: -2.5rem; top: 0.3125rem; color: rgb(153, 153, 153); border-color: rgb(153, 153, 153); }
.md-toc:focus .md-toc-content { margin-top: 19px; }
.md-toc-content:empty::before { color: rgb(6, 85, 136); }
.md-toc-item { color: rgb(6, 85, 136); }
#write div.md-toc-tooltip { background-color: rgb(243, 242, 238); }
#outline-dropmenu { background-color: rgb(243, 242, 238); -webkit-box-shadow: rgba(0, 0, 0, 0.372549) 0px 6px 12px; box-shadow: rgba(0, 0, 0, 0.372549) 0px 6px 12px; }
.pin-outline #outline-dropmenu { background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: inherit; box-shadow: none; border-right-width: 1px; border-right-style: dashed; background-position: inherit inherit; background-repeat: inherit inherit; }
.pin-outline #outline-dropmenu:hover .outline-title-wrapper { border-left-width: 1px; border-left-style: dashed; }
.outline-item:hover { background-color: rgb(218, 218, 218); border-left-width: 18px; border-left-style: solid; border-left-color: rgb(218, 218, 218); border-right-width: 18px; border-right-style: solid; border-right-color: rgb(218, 218, 218); }
.outline-expander::before { content: ''; font-family: FontAwesome; font-size: 14px; top: 1px; }
.outline-expander:hover::before, .outline-item-open > .outline-item > .outline-expander::before { content: ''; }

又开始了这个问题的讨论,哈哈,直接迁移到swift??这个问题在ef oc 2.0中也有过列举各自的一些优缺点.

原文链接

The Debate Over Direct Access 变量使用的争议

At lunch today a few of us discussed the issue of using self.foo vs. _foo in Objective-C.

We had people on two sides. I’ll lay out the arguments.

(Note: this isn’t even a debate in Swift, which is one of the reasons I’m eager to switch to Swift.)

self.foo

This side argues against declaring ivars, and argues that all properties — external and internal — should be synthesized (usually implicitly).

The only cases where you access the underlying storage directly — reference _foo, in other words — is in init, dealloc, and in custom accessors. Otherwise you use self.foo everywhere.

除了在init,dealloc ,自定义的访问方法中,其他的地方都使用self.的形式.

Reasons:

  • It’s a simple rule to remember. You don’t have to remember whether a property is internal or external.(便于记忆)
  • A given property can have custom accessors, or not, and you still treat it the exact same way. Adding or removing custom accessors does not mean you have to go looking for all the references to that property and possibly change them.(修改方便)
  • You’re treating your object’s interface as an API. Inside the object you have more API than outside callers can see, which is fine. It’s still all API.(作为API访问)
  • You have to worry less about KVO if you always use self.foo instead of _foo.(不用担心KVO)
  • You’re more likely to get memory management right if you use self.foo. (This is much less of an issue with ARC, I grant.)(手动内存管理的时候,更加方便.)
  • Subclasses are more likely to get things right if you use self.foo.(子类化方便)
  • Apple seems to advocate this style. (Not always consistently.)(Apple推荐....)

_foo

This side argues that using direct storage access inside an object is the way to go.

Reasons:

  • There’s a useful distinction between public and private. The code for an object is private, and it’s therefore fair to access storage directly. An object has one API — its public API — and inside the object you can do whatever makes sense.(公私分明)
  • Any time you send a message, it’s possible that anything could happen, including reentrancy bugs and so on. Accessing storage directly does not have that problem.(容易引入bug)
  • Sending a message may have performance issues. (Probably not. But it’s possible.)(可能会存在性能问题)

Okay — I don’t fully understand this side of the argument. I did the best I can to explain it, but I’m most definitely in the self.foo camp.

But smart people disagree with me.

Why am I wrong, and why is _foo better?

undefined

变量使用self.foo还是_foo的更多相关文章

  1. Python变量的命名 单下划线和双下划线

    python命名变量的区别 foo: 一种约定,Python内部的名字,用来区别其他用户自定义的命名,以防冲突,就是例如__init__(),__del__(),__call__()这些特殊方法 _f ...

  2. PHP变量入门教程(3)global 关键字

    global关键字 首先,一个使用 global 的例子: 使用 global <?php $a = 1; $b = 2; function Sum() { global $a, $b; $b ...

  3. PHP变量作用域详解(二)

    学过C的人用PHP的时候一般会相当顺手,而且感到PHP太方便太轻松.但在变量作用域这方面却与C有不同的地方,搞不好会相当郁闷,就找不到错误所在.昨晚就与到这么一个问题,是全局变量在函数中的问题.今天搜 ...

  4. PHP的变量

    1.可变变量 一个变量的变量名可以动态地设置和使用.一个普通的变量通过声明来设置,而一个可变变量获取了一个普通变量的值作为这个可变变量的变量名,如下所示: <?php $hi = "h ...

  5. makefile变量赋值

    在定义变量的值时,我们可以使用其它变量来构造变量的值,在Makefile中有两种方式来在用变量定义变量的值. 先看第一种方式,也就是简单的使用“=”号,在“=”左侧是变量,右侧是变量的值,右侧变量的值 ...

  6. Js变量定义——fn里 var与不var的区别

    js运行时内置了一个Global对象. 这个Global对象跟运行环境有关.在浏览器运行环境中.Global就是window对象.在nodejs中.Global对象是global对象. 当你在浏览器环 ...

  7. 【JS笔记】私有变量

    1.任何函数中定义的变量都可以认为是私有变量.函数内部可以访问,外部不能访问. 可以通过闭包创建特权方法访问私有变量. function Foo(){ var n=10; this.returnN=f ...

  8. 跟我一起写Makefile--- 变量(嵌套变量+追加变量+overrid+多行变量+环境变量+目标变量+模式变量)

    目录(?)[-] 使用变量 一变量的基础 二变量中的变量 三变量高级用法 四追加变量值 五override 指示符 六多行变量 七环境变量 八目标变量 九模式变量 使用变量 ———— 在Makefil ...

  9. Linux makefile教程之使用变量五[转]

    使用变量 ———— 在 Makefile中的定义的变量,就像是C/C++语言中的宏一样,他代表了一个文本字串,在Makefile中执行的时候其会自动原模原样地展开在所使 用的地方.其与C/C++所不同 ...

随机推荐

  1. API接口规范

    协议 API与用户的通信协议,总是使用HTTPs协议,确保交互数据的传输安全. 域名 应该尽量将API部署在专用域名之下. https://api.example.com 如果确定API很简单,不会有 ...

  2. List遍历Java 8 Streams map() examples

    1. A List of Strings to Uppercase 1.1 Simple Java example to convert a list of Strings to upper case ...

  3. 翻译Java虚拟机的结构

    英文原版:  https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-2.html 直接谷歌翻译: Java SE规范 > Java虚拟机 ...

  4. flowable 的ProcessEngine配置

    1 flowable process engine 是通过  flowable.cfg.xml 配置文件配置的.在spring 环境中是使用 flowable-context.xml 配置文件的, P ...

  5. 关于easyui combobox下拉框实现多选框的实现

    好长时间没有更博了,一是因为最近真的比较忙,二是因为自己是真的偷懒了,哈哈 好啦,这篇博客主要是总结一些关于easyui combobox下拉框实现多选框的实现,包括前台界面的展示,和后台对数据的获取 ...

  6. java Web的MVC最基础暂定分层包

    数据封装 entity, 数据访问对象  Dao, 业务逻辑 servlet, ----- 网页显示层 jsp 加上 jsp附带技术 el表达式和jstl ,jsp 标记库语言, el表达式 ${us ...

  7. JAVA之堆内存和栈内存的差别

    欢迎转载.请附上出处: http://blog.csdn.net/as02446418/article/details/47007975 笔者近期在准备面试的时候又一次看了一些JAVA基础的知识,以下 ...

  8. [LeetCode] Basic Calculator & Basic Calculator II

    Basic Calculator Implement a basic calculator to evaluate a simple expression string. The expression ...

  9. 微信小程序实现给循环列表添加点击样式实例

    微信小程序有个属性hover-class='active',是指当点击列表元素时当按下鼠标左键会显示active样式,但是鼠标离开样式就会复原.可以参考以下解决方案,直接上代码: wxml: ? 1 ...

  10. FTP整站上传的批处理脚本

    一个FTP整站上传的批处理代码.例子: @echo off rem 设置FTP服务器地址 set ftpIP=192.168.0.2 rem 设置FTP用户名 set ftpUser=MyUser r ...