php 运算符当作变量要怎么做

Basics

Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive.

Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'

Note: For our purposes here, a letter is a-z, A-Z, and the bytes from 127 through 255 (0x7f-0xff).
Note: $this is a special variable that can't be assigned.

你是要 实现这样？
```php
$a = 1;
$b = 1;
$c = '-';
echo $a.$c.$b;//1-1
echo eval("return {$a}{$c}{$b};");//0
```
但是 eval 函数在很多情况下会被禁用

switch 吧

自己动手撸个 parser