为什么在MATLAB中允许使用多个连续的加号语法? [英] Why are multiple, consecutive plusses allowable syntax in MATLAB?

问题描述

有人知道为什么它可以在MATLAB中工作吗?

Does anyone know why this works in MATLAB?

>> 1 ++ 2
ans =
     3

来自C，python，Java等语言的编码，我发现这完全可以反常觉.大概解析器有一些我不了解的重要内容?

Coming from coding in C, python, Java etc, I find it most counterintuitive that this should work at all. Presumably there's something important about the parser that I don't understand?

推荐答案

plus 和 uplus .我怀疑MATLAB将第一个+用作plus，而所有其他的作为uplus.由于默认情况下uplus只是返回后面的内容"，因此您添加1和2，并在两者之间使用很多返回后面的内容".

There's a difference between plus and uplus. I suspect MATLAB takes the first + as plus, and all the others as uplus. Since uplus is by default just "return what's behind", you add 1 and 2, and use a lot of "return what's behind" in between.

a=2;
c=+a % unitary plus
c =
     2
1+2 % addition
ans =
     3
1+++2 % addition and two uplusses
ans =
     3

存在uplus的原因是允许操作符在类中重载.同样的语言也适用于其他语言，例如在C#中，以允许操作员在受限类中重载.

The reason uplus exists is to allow operator overloading in classes. The same works in other languages, e.g. in C#, to allow for operator overloading in confined classes.

在该C#线程中提到的另一个原因是将无符号短裤更改为整数，而对于MATLAB则不是这种情况:

The other reason mentioned in that C# thread is that is changes unsigned shorts to integers, which is not the case for MATLAB:

d=uint8(1)
d =
  uint8
   1
+d
ans =
  uint8
   1
a=+d
a =
  uint8
   1

但是，由于

It does, however, convert a boolean to a double, thanks to Cris Lunego for pointing that out:

+true
ans =
     1
+false
ans =
     0

---

以下内容对我来说仍然是一个谜，灵感来自相同的方法适用于多个加号[1 +++..+++ 2]，因此所有加号在中间连续产生[1 2]，所有其他组合(据我测试)均为3.我问了一个与此有关的单独问题:为什么加号和一元加号在数组语法中表现出奇怪的特征?

The same works with multiple plusses, [1 +++..+++ 2], so with all plusses consecutively in the middle generates [1 2], all other combinations (as far as I tested) result in 3. I asked a separate question about this: Why do the plus and unary plus behave strange in array syntax?

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