JavaScript幂运算一元运算符的设计决策 [英] JavaScript exponentiation unary operator design decision

问题描述

因此，我正与新的幂运算符鬼混，发现不能在基数前紧跟一元运算符.

So I was fooling around with the new exponentiation operator and I discovered you cannot put a unary operator immediately before the base number.

let result = -2 ** 2; // syntax error
let result = -(2 ** 2); // -4
let x = 3;
let result = --x ** 2; // 4

摘自MDN上的文档:

在JavaScript中，不可能编写模棱两可的幂表达式，即不能放置一元运算符(+/-/~/!/delete/void/)紧接在基数之前.

In JavaScript, it is impossible to write an ambiguous exponentiation expression, i.e. you cannot put a unary operator (+/-/~/!/delete/void/typeof) immediately before the base number.

在大多数语言中，例如PHP和Python以及其他具有指数运算符的语言(通常为^或**)，指数运算符的定义优先级高于一元运算符(例如一元+和一元-，但也有一些例外.例如，在Bash中，**运算符被定义为具有比一元运算符更低的优先级.

In most languages like PHP and Python and others that have an exponentiation operator (typically ^ or **), the exponentiation operator is defined to have a higher precedence than unary operators such as unary + and unary -, but there are a few exceptions. For example, in Bash the ** operator is defined to have a lower precedence than unary operators.

我知道这是设计使错误.我不明白这个设计决定.谁真的会对-x ** 2为负数感到惊讶?这不仅遵循了其他主流编程语言，而且遵循了数百年来普遍使用的数学符号，并且这种数学符号已向每位高中代数学生教授.

I understand this was made an error by design. I don't understand this design decision. Who's really going to be surprised that -x ** 2 is negative? This follows not only other mainstream programming languages but a mathematical notation that has been in common use for hundreds of years and is taught to every high school algebra student.

在Javascript中，'1'+ 2是'12'，而'1'-2是-1，但是-1**2会引发错误，因为它可能是模棱两可的?帮助我了解这个设计决定.

In Javascript '1'+ 2 is '12' and '1'-2 is -1 but -1**2 raises an error because it could be ambiguous? Help me understand this design decision.

推荐答案

我不明白这个设计决定.

I don't understand this design decision.

有关详细信息，请访问 https://esdiscuss.org/topic/exponentiation-operator-precedence ， https://esdiscuss.org/topic/power-operator-why-does-2-3-throws ， https://github.com/rwaldron/tc39-notes/blob/master/es7/2015-09/sept-24.md#exponentiation-operator .

Read more about it at https://esdiscuss.org/topic/exponentiation-operator-precedence, https://esdiscuss.org/topic/power-operator-why-does-2-3-throws, https://github.com/rwaldron/tc39-notes/blob/master/es7/2015-09/sept-23.md#exponentiation-operator and https://github.com/rwaldron/tc39-notes/blob/master/es7/2015-09/sept-24.md#exponentiation-operator.

-x ** 2是否为负真的会让谁感到惊讶?

Who's really going to be surprised that -x ** 2 is negative?

足够重要的人.以上资源中的一些相关引用:

Enough people to matter. Some relevant quotes from the above resources:

• "使**绑定比一元运算符更紧密会破坏x**-2.有时使其变得更紧密有时更松散会太混乱，并导致其他优先级倒置的机会."- Waldemar Horwat
• "鉴于其他语言**的历史之间的冲突，以及[]一元绑定比二进制绑定更严格的一般模式，此时的任何解决方案都会使许多人感到困惑."- 马克·米勒
• "确认存在大量空白的可能性:-x**2 === -(x ** 2)和-x ** 2 === (-x) ** 2 "-问题是，无论在取幂表达式之前出现一元负数是多少，都是因为缺少-比**绑定更紧密的上标和较小的字体，所以实际上除了点(特殊形式，其右操作数必须是词法标识符名)和方括号(本身不是infix运算符)，在C和其他C派生语言中，一元运算符在JS中的绑定比二进制更紧密.- Brendan Eich
• "在数学上，显然-52.但是对于-5 ** 2，由于infix运算符周围有空格.即使没有空格，-似乎也是文字的一部分."-戴夫·赫尔曼(Dave Herman)
• [关于编程语言的优先顺序]，"实际上零人对其他语言有这种理解.同意人们对**是幂运算符的理解.但是人们通常会尽量避免出现黑角，因此永远不要为否定的基础发展直觉."-戴夫·赫尔曼

• "making ** bind tighter than unary operators would break x**-2. And making it sometimes tighter and sometimes looser would be too confusing and lead to other opportunities for precedence inversion." - Waldemar Horwat
• "Given the conflict between the history of ** in other languages, [and] the general pattern that unary binds tighter than binary, any solution at this point will confuse many people." - Mark S. Miller
• "acknowledge the prospect of significant whitespace: -x**2 === -(x ** 2) and -x ** 2 === (-x) ** 2" - Alexander Jones
• "The problem is, however rare unary minus before an exponentiation expression may be, the lack of superscript-with-smaller-font sugests that - binds tighter than **. And indeed apart from dot (a special form whose right operand must be a lexical identifier-name) and square brackets (which isn't an infix operator per se), unary operators bind tighter than binary in JS as in C and other C-derived languages." - Brendan Eich
• "For math it seems obvious that -52. But for -5 ** 2, because of the whitespace around the infix operator. Even without space, - seems to be part of the literal." - Dave Herman
• [Regarding programming language precedence], "effectively zero people have an intutition about this from other languages. Agree people have an itutition that ** is the exponentiation operator. But people usually try to avoid dark corners so they never develop an intuition for negative bases." - Dave Herman

在Javascript中，'1'+ 2是'12'，而'1'-2是-1，但是-1**2会引发错误，因为它可能是模棱两可的?

In Javascript '1'+ 2 is '12' and '1'-2 is -1 but -1**2 raises an error because it could be ambiguous?

他们今天在语言扩展设计上投入了更多的精力:-)这是他们达成共识的最佳解决方案.

Well they put considerably more effort in the design of extensions to the language today :-) It's the best solution that they could reach consensus for.

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