Question

I just saw this source code on a website, but I don’t know what it means, can anyone tell me what it is? thank you so much.

private function buildCache()
{
    !empty($this->cache_list) && $this->cache->loadCache($this->cache_list);
}

Answer 1

It is the example of bad code which is hard to support.

The !empty($this->cache_list) && $this->cache->loadCache($this->cache_list); statement is equivalent to $dummy = !empty($this->cache_list) && $this->cache->loadCache($this->cache_list);.

There is such thing as lazy evaluation, so that in A && B, B will be evaluated only is A is true (otherwise A && B is knowingly false and there is no need to evaluate B). Basically, $x = a() && b() is the same as

$x = true;
if(!a()) {
    $x = false;
} else {
    $x = b();
}

Thus, we can expand the original statement as

$dummy = true;
if(empty($this->cache_list)) {
    $dummy = false;
} else {
    $dummy = $this->cache->loadCache($this->cache_list);
}

which, remembering that we don’t need the $dummy variable, is the same as

if(!empty($this->cache_list)) {
    $this->cache->loadCache($this->cache_list);
}

Despite this code is 2 lines longer than the original one, it is much easier to understand and to mantain. You should write the code which is like this final version and avoid writing anything like the original one-liner.

You can see it by yourself: while it was hard for you to tell what is going on in the original one-liner (so hard that you had to ask the question on SO), it is quite easy to see what is going on in the final version: if the cache_list is not empty, we’re calling loadCache passing cache_list to it as the argument (otherwise, if the cache_list would be empty, it would probably be pointless to call loadCache passing empty value to it as the argument).