为什么后缀++ / - 归类为C＃的主要运营商？ [英] Why are Postfix ++/-- categorized as primary Operators in C#?

问题描述

目前我教一类的C ++程序员的C＃语言的基础知识。正如我们讨论的话题运营商我使用的主，一元等运营商的C＃标准类别。

Currently I'm teaching a class of C++ programmers the basics of the C# language. As we discussed the topic operators I used C# standard categories of primary, unary etc. operators.

一位与会者感到不解，因为在C＃标准后缀+ + / - 已投入在主运营商的类别，而不是前缀+ + / - 。她的这种混乱背后的理由是，她宁愿实现C ++运算符后缀++ / - 的在的操作前缀++ / - 的条款。换句话说，她宁愿指望运营商前缀++ / - 作为一个主要的运营商。 - 我明白了她的观点，但我不能给她背后的理由。确定的运算符后缀++ / - 具有比前缀+ + / - 的优先级高？，但这是后面的唯一理

One of the attendees felt puzzled, because in the C# standard the "postfix ++/--" have been put in the category of primary operators rather than the "prefix ++/--". Her rationale behind this confusion was, that she would rather implement the C++ operator "postfix ++/--" in terms of the operator "prefix ++/--". In other words she would rather count the operator "prefix ++/--" as a primary operator. - I understand her point, but I can't give to her a rationale behind that. OK the operators "postfix ++/--" have a higher precedence than "prefix ++/--", but is this the only rationale behind that?

的。规范章节14.2.1运算符优先级和结合提到

The spec mentioned it in section "14.2.1 Operator precedence and associativity".

所以，我很中性的问题：为什么后缀++ / - 归类为C＃的主要运营商？
是有它更深的道理吗？

So my very neutral question: Why are Postfix ++/-- categorized as primary Operators in C#? Is there a deeper truth in it?

推荐答案

由于ECMA标准本身并没有定义什么是主要运算符，比位次（即来临前'一元'）不可能有其他的意义等。词的选择可能是坏的。

Since the ECMA standard itself does not define what a 'Primary' operator is, other than order of precedence (i.e. coming before 'Unary') there can be no other significance. The choice of words was probably bad.

考虑到，在许多C-链接语言，后缀运营商往往会创造一个表达式的中间结果存储在临时变量（请参阅：首选运营商前缀后缀上以分号）。因此，他们是由前缀版本有着根本的不同。

Take into account that in many C-link languages, postfix operators tend to create a temporary variable where the expression's intermediate result is stored (see: "Prefer prefix operators over postfix" at Semicolon). Thus, they are fundamentally different from the prefix version.

不过，快速检查单和Visual Studio如何编译for循环使用后缀和前缀形式，我看到产生的IL代码是相同的。只有当你使用后缀/前缀表达式的值它翻译成不同的IL（仅影响其中的'DUP'指令放置），至少在这些实现提及。

Nonetheless, quickly checking how Mono and Visual Studio compile for-loops using the postfix and prefix forms, I saw that the IL code produced is identical. Only if you use the postfix/prefix expression's value does it translate to different IL (only affecting where the 'dup' instruction in placed), at least with those implementations mentioned.

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