为什么data.table定义了：=而不是重载< - ？ [英] Why has data.table defined := rather than overloading &lt;-?

问题描述

data.table已经引入了：=运算符。为什么不重载< - ？

data.table has introduced the := operator. Why not overload <-?

推荐答案

我认为没有任何技术原因，原因：：= 仅在 [...] 内使用，因此始终使用引号。 [...] 通过表达式树查看：= 是否在其中。

I don't think there is any technical reason this should be necessary, for the following reason: := is only used inside [...] so it is always quoted. [...] goes through the expression tree to see if := is in it.

这意味着它不是真正的作为一个运算符，它不是真的重载;所以他们可以选择几乎任何他们想要的操作员。我想也许它看起来更好？或者较少混淆，因为它显然不是< - ？

That means it's not really acting as an operator and it's not really overloaded; so they could have picked pretty much any operator they wanted. I guess maybe it looked better? Or less confusing because it's clearly not <-?

= c 之外 使用 ，因为您实际上不能重载 < - 。 t评估其左边的参数，所以它不知道什么类型是）。

(Note that if := were used outside of [...] it could not be <-, because you can't actually overload <-. <- Doesn't evaluate its lefthand argument so it doesn't know what the type is).

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