R赋值运算符:=的作用是什么? [英] What is the R assignment operator := for?

问题描述

通过深入研究R源代码(文件R-3.2.2/src/main/gram.y行2836至2852)，我发现R分析器/令牌器认为:=是LEFT_ASSIGNMENT令牌.

By digging into R source code (file R-3.2.2/src/main/gram.y lines 2836 to 2852) I found that the R parser/tokenizer considers that := is a LEFT_ASSIGNMENT token.

但是在R.3.2.2中尝试将其用作赋值运算符时，
我有一个错误(无法找到:=的函数...)，但是正如您所看到的，R会将其视为类似<-的赋值:

But when trying to use it as an assignment operator in R.3.2.2,
I have an error (impossible to find function for := ...) but as you can see R considers it as an assignment like <- :

> myVar := 42
Erreur : impossible de trouver la fonction ":="
> :=
Erreur : unexpected assignment in ":="
> <-
Erreur : unexpected assignment in "<-"

是错误，还是需要从令牌生成器源代码中删除令牌:=?

Is it a bug, or does the token := need to be removed from the tokenizer source code?

R中是否有关于:=运算符的故事?

Is there a past story about := operator in R?

推荐答案

它是以前允许的赋值运算符，请参见本文来自约翰·钱伯斯(John Chambers)在2001年.

It was a previously allowed assignment operator, see this article from John Chambers in 2001.

R的开发版本现在允许编写一些作业 使用=运算符的C或Java样式.这增加了兼容性 使用S-Plus(以及C，Java和许多其他语言).

The development version of R now allows some assignments to be written C- or Java-style, using the = operator. This increases compatibility with S-Plus (as well as with C, Java, and many other languages).

所有先前允许的赋值运算符(<-，:=，_和<< ;-) 保持完全有效.

All the previously allowed assignment operators (<-, :=, _, and <<-) remain fully in effect.

似乎:=功能不再存在，但是您可以像这样重新启用"该功能:

It seems the := function is no longer present, but you can "re-enable it" like this:

`:=` <- `<-`
x:=3
x
[1] 3

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