问题
I have the following code snippet where I don't really understand its output:
echo 20...7;
Why does this code output 200.7?
From what I know ... is the splat operator, which it is called in ruby, that lets you have a function with a variable number of arguments, but I don't understand what it does here in the context with echo.
Can anyone explain what exactly this code does?
回答1:
No this is not the splat/unpacking operator, even thought it might seem like it is. This is just the result of the PHP parsing process. Already writing your code a bit different might clear some confusion:
echo 20. . .7;
# ↑ ↑ ↑
# decimal concatenation decimal
# dot dot dot
Now you have to know that .7 is 0.7 and you can omit the 0 in PHP as described in the syntax for float numbers:
DNUM ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
So PHP just concatenates those two numbers together and while doing this PHP's type juggling will silently convert both numbers to strings.
So in the end your code is equivalent to:
echo "20" . "0.7";
//Output: "200.7"
来源：https://stackoverflow.com/questions/44023765/why-is-concatenating-two-numbers-in-my-code