Ford, Mike wrote: > On 06 November 2007 12:57, Christoph Boget wrote: > >> Consider the following test code: > > [...snip...] > >> Running that I found that >> >> if( isset( $myArray[$key] )) >> >> is faster than >> >> if( array key exists( $key, $myArray )) >> >> is faster than >> >> if( $myArray[$key] ) >> >> To be honest, I was surprised. I would have thought that if( >> $myArray[$key] ) would have been the fastest way to check. I'm >> wondering if those in the know could explain why it's the slowest and >> also where the discrepancies come from w/r/t the difference in the >> amount of time it takes >> to make each >> check. > > OK, I'll take a stab. > > Firstly, isset() is a language construct not an actual function, so the only > thing your isset() does is check whether the array element exists. > > Next, array_key_exists() is the only one that involves a real function call, > so it's going to bear that cost. However, the function then does a pretty > simple test which again only involves checking whether the key exists, so the > function itself is going to be pretty quick. > > Finally, the if() is the only one that actually gets the value in > $myArray[$key], and then casts it to Boolean to boot, and the cost of this > must therefore outweigh the cost of a function call plus a check for a key's > existence. > > I'm certainly not surprised that isset() is the quickest, because it does the > simplest test, but to be honest I'm not sure if I'd have predicted the > relative positions of the other two.. > > Cheers! > > Mike >
For convenience let's label the cases: 1: if( isset( $myArray[$key] )) 2: if( array key exists( $key, $myArray )) 3: if( $myArray[$key] ) Now, surely 3 is not comparable at all to 1 and 2. Cases 1 and 2 check that the key exists in the array. Case 3 does a boolean test on the value referenced by the key. That has several consequences: Firstly, if there is no element with key "$key" in the arrray, the interpreter will throw an error (undefined index ...); this error could be suppressed and ignored, I suppose. Secondly, if the value referenced by the key is equivalent to FALSE, then the test will return FALSE; for example, if you have set $myArray[$key]='' or $myArray[$key]=0. This could be very confusing. So if you want to test that the key exists, case 3 is NOT the way to do it. In fact, you will often want to check that the key exists(with case 1, ideally) BEFORE using a test of the form of case 3. Cheers Pete Ford (no relation, I think, although I do have a cousin called Michael...) -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
