Simple generalization of the difference between single and double quotes in a PHP string _php tips

Today, a friend asked, the next difference, by the way review.

Single quotes differ from double quotes:

• The fields inside the double quotes are interpreted by the compiler and then exported as HTML code.
• ' Single quotes inside without explanation, direct output.
• Single quotes parse more quickly than double quotes.
• Single quotes support \ Escape characters, double quotes support more escape characters.

$hello = 3;
echo "Hello is $hello"; Print Result: Hello is 3 
echo ' Hello is $hello ';//print Result: Hello is $hello 
echo "Hello is $hello \ n";//Print Result: Hello is 2 (line wrap at the same time) 
Echo ' Hello is $hello \ n '; Print Result: Hello is $hello \ n

Ps:
today, I saw a foreigner mention the single quotation mark of PHP, which mentions the interesting things, excerpt as follows:
Which said that installed PHP expansion Vulcan Logic disassembler, you can see the middle code generated by PHP,
The first is:

echo "This is a string"; 

Will turn into:

ECHO    ' This is a string ' 

and

Echo ' is a string '; 

It becomes

 ECHO    ' This is a string ' 

, is the same
If it is

echo "This is a $variable"; 

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 A dd_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; 

It will become

CONCAT    ~0 ' This is a '!0 

2 ECHO      ~0 

You can see, the speed is much faster, use. Connection words