A brief summary of the difference between single quotes and double quotes in PHP strings_php tips

Today a friend asked me about the difference and I would like to review it by the way.

The difference between single quotes and double quotes:

• " "Fields enclosed in double quotes will be interpreted by the compiler and then output as HTML code.
• ' 'The words inside the single quotes are not interpreted and are output directly.
• Single quotes are parsed faster than double quotes.
• Single quotes support escape characters, and double quotes support more escape characters.

$hello= 3;
echo "hello is $hello"; // 打印结果:hello is 3 
echo 'hello is $hello'; // 打印结果: hello is $hello 
echo "hello is $hello\n"; // 打印结果: hello is 2 (同时换行) 
echo 'hello is $hello\n'; // 打印结果: hello is $hello\n

PS:
Today I saw a foreigner mentioning the issue of single quotes in PHP, and he mentioned something interesting. The excerpt is as follows:
It says that after installing the PHP extension Vulcan Logic Disassembler, you can see the intermediate code generated by PHP,
The first is:

echo "This is a string"; 

will transform into:

ECHO    'This is a string' 

and

echo 'This is a string'; 

becomes

 ECHO    'This is a string' 

, it’s the same
If it is

echo "This is a $variable"; 

Then the OPCODE generated by PHP is

INIT STRING ~0 

2 ADD_STRING  ~0 ~0 'This' 

3 ADD_STRING  ~0 ~0 ' ' 

4 ADD_STRING  ~0 ~0 'is' 

5 ADD_STRING  ~0 ~0 ' ' 

6 ADD_STRING  ~0 ~0 'a' 

7 ADD_STRING  ~0 ~0 ' ' 

8 ADD_VAR    ~0 ~0 !0 

9 ECHO      ~0 

and

echo "This is a " . $variable; 

will become

CONCAT    ~0 'This is a ' !0 

2 ECHO      ~0 

As you can see, the speed is much faster. If you use. to connect