Question

I noticed that many developers use Math operations as variable values, like:

$time = 60 * 60 * 24 * 7; // 7 days

instead of just assigning the computed value

$time = 604800;

I know it makes the code more easy to understand, but won’t this affect performance?
Do you think it’s a good practice to do this?

Answer 1

In a compiled language there would be no performance penalty as the calculation would be done at compile time. PHP generally is not compiled so there’s probably a small performance penalty. In most cases I would prefer more readable code to higher performance (unless the code becomes a bottleneck). So DON’T worry about performance in this case.

Now if we compare your examples then

$time = 60 * 60 * 24 * 7;

is self explanatory even without a comment. If you write

$time = 604800;

then it’s not obvious, what the value represents. Now, you could add a comment and write

$time = 604800; // 7 days in seconds

but this is bad for two reasons:

1. you are duplicating information, which is maybe not a big problem in itself, but
2. if you change the value without a modifying a comment, then you have harmful comment in your code. This is much bigger problem and is really caused by information duplication.