What will php's var_dump(1...9) output?

What will var_dump(1...9) output? The following article will analyze it for you. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

A question, var_dump(1...9)What is the output?

Verify it by hand:

php -r “var_dump(1...9)”;
string(4) ”10.9“

Output 10.9. At first glance, the output of this var_dump seems strange, right? why?

Here we will teach you, if you see a piece of PHP code and feel that the output is strange, the first reaction is to see what the opcodes generated by this code are. Although this problem is actually a problem in the lexical analysis stage, but still use Let's analyze it with phpdbg (usually in order to prevent the influence of opcache, -n will be passed):

phpdbg -n -p /tmp/1.php
function name: (null)
L1-35 {main}() /tmp/1.php - 0x7f56d1a63460 + 4 ops
L2 #0 INIT_FCALL<1> 96 "var_dump"
L2 #1 SEND_VAL "10.9" 1
L2 #2 DO_ICALL
L35 #3 RETURN<-1> 1

So it seems that long before the opcode is generated, 1...9 becomes the constant 10.9, considering This is a literal value. Let’s take a look at zend_language_scanner.l and find this line:

DNUM ({LNUM}?"."{LNUM})|({LNUM}"."{LNUM}?)

This is the format of floating point numbers defined by lexical analysis. It suddenly dawned on us at this point:

1 ...9 will be accepted in sequence as: 1. (floating point number 1), then . (string concatenation symbol) and then .9 (floating point number 0.9)

so it will be generated directly during the compilation phase "1" . "0.9" -> String literal "10.9"

Okay, here, this little "puzzle" is explained clearly.

Of course, this is not only defined in PHP, almost all languages ​​will define this abbreviated floating-point form. Sometimes in C language, in order to input a floating-point integer, we can Use for example 1. to tell the compiler that this is a floating point number.

However, firstly, it happens to be in PHP. The number has another meaning, which is string concatenation. Secondly... in PHP5.6 Then there is a new operator called the Splat operator, which can be used to define variable parameter functions or solve arrays, for example,

<?php
 
function  foo($a, $b, $c) {
        var_dump($a + $b + $c);
}
 
 
$parameters = array (1, 2, 3);
 
foo(...$parameters);
?>

So, at first glance, this leads to this confusing result

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