This is a test.

Qualsys is offering a free SSL testing service here:

https://www.ssllabs.com/index.html

Some have claimed that double-quoted string evaluation in PHP run at the same speed as single-quoted (or constant) string evaluation. As a reminder, double-quoted strings are useful because they permit variables to be evaluated inside of them, whereas single-quoted strings do not.

Below I will consider the veracity of the claim.

Let us consider three cases:

1. A constant string at the end of which we append another string.
2. A constant string in the middle of which we insert another string.
3. A constant string by itself.

Case 1

Consider this PHP program:

$a = 5; for ($i = 0; $i < 10000000; $i++) { echo "This is a test $a"; }

versus this equivalent program:

$a = 5; for ($i = 0; $i < 10000000; $i++) { echo 'This is a test' . $a; }

In this test, a common situation occurs in which a variable is included within a double-quoted string. The single-quoted equivalent requires that we concatenate a constant string and the variable.

At the command-line, we can run each of these programs and get the execution times for each like so:

time php ./program.php > /dev/null

The result is as follows:

In three runs of the double-quoted string program, I got times of:

49, 47 and 42 seconds. (Average 46 sec.)

In three runs of the single-quoted string program, I got userland running times of:

37, 40, and 40 seconds. (Average 39 seconds.)

This means the double-quoted string program ran 18% longer (slower) than the single-quoted equivalent.

Case 2

Now let's consider the case of inserting a string inside of a constant string:

$a = 5; for ($i = 0; $i < 10000000; $i++) { echo "This is a test $a etc."; }

versus this equivalent program:

$a = 5; for ($i = 0; $i < 10000000; $i++) { echo 'This is a test' . $a . 'etc.'; }

Times for the double-quoted program (7 runs) are 51, 48, 46, 51, 46, 51, 46 for an average of 48.

Times for the single-quoted program (7 runs) are 47, 47, 46, 44, 43, 44, 44, for an average of 45.

In this case, double-quoted strings were evaluated only 7% slower than single-quoted.

Case 3

Finally let's consider simple constant strings:

for ($i = 0; $i < 10000000; $i++) echo "This is a test etc.";

versus this equivalent program:

for ($i = 0; $i < 10000000; $i++) echo 'This is a test etc.';

These two run at essentially the same speed, as is to be expected because PHP converts the source code into an internal, compiled format that expresses a double-quoted constant string that lacks variables expressions within it the same as a single-quoted string.

Double-quoted times: 22, 22, 21, 21, 22, 21, 22 seconds for an average of about 22.

Single-quoted times: 21, 21, 23, 22, 22, 22, 22 seconds for an average of 22.

Conclusion

The claim that single- and double-quoted strings evaluate at the same speed is true if and only if the double-quoted strings do not contain any variable expressions. This is an important qualification, because double-quoted strings are often used with variable expressions inside of them.

Researchers have been looking at what Facebook does for people and what it doesn't do. A coherent image is beginning to form.

In England, Dr. Sam Roberts found that Facebook does not win you new friends, nor does it improve your existing relationships.

http://www.abc.net.au/radionational/programs/scienceshow/...

In Australia, researchers Ryan and Xenos determined that narcissistic, exhibitionist, and extrovert personalities are drawn to Facebook.

http://dl.acm.org/citation.cfm?id=2007616

Boston researchers Nadkarni and Hoffman found that the need to belong and the need for exhibitionism drive Facebook use.

http://docs.google.com/viewer?a=v&q=cache:caZkTNJLnRoJ:bi...

Researchers Kirschner and Karpinski in the Netherlands and the USA respectively found that Facebook users have lower GPAs and study less.

http://www.sciencedirect.com/science/article/pii/S0747563...

This correlation between poor academic performance and studying habits on the one hand and Facebook use was confirmed in a larger study by Junco, in the USA.

http://www.sciencedirect.com/science/article/pii/S0747563...