Builder Pattern rocks, as @maple_shaft said. I would agree that that would be the best answer in most cases, but the Builder pattern is best suited when many parameters are optional and it can require a fair amount of up-front programming work to make your API easy to use for your clients. For completeness I feel I should mention some other options.
#Named Parameter Map class MyApi { const Param1Name = 0; const Param2Name = 1; // etc.
public function sampleApiMethod($myParamHash) { //Method Code $localParam1 = $myParamHash[Param1Name] } } // Load up params using pre-defined symbolic names to prevent typos $myParamHash = array (MyApi::Param1Name => 5, MyApi::Param2Name => 9); // call method sampleApiMethod($myParamHash); Maybe that's what you are doing already when you say "array." If so, I like that you separate out the required options from the optional ones. The beauty of this option (or the builder) is that it makes it clear which parameter is which, thus avoiding a lot of potential errors.
#Default Values I just did a quick search, and it seems that PHP supports default values for arguments. These are probably better than Telescoping Methods, but there may be some cases where telescoping works and default values don't so...
#Telescoping Methods Not sure if this works in php, but Something like:
public function sampleApiMethod($reqVal1, $reqVal2, $additionalOptions) { //Method Code } public function sampleApiMethod($reqVal1, $reqVal2) { sampleApiMethod($reqVal1, $reqVal2, null); } public function sampleApiMethod($reqVal1) { sampleApiMethod($reqVal1, null, null); } I'm using "null" for default values. But for an API, this makes things much easier on the caller without the work of creating a builder. Just put the most commonly used arguments first and provide sensible defaults in your telescoping methods.
#Model Almost all useful programs model some real-world things or actions. An API that takes 30 parameters strikes me as a red flag that there may be some higher-level design issues in your API. You might want to provide a model for some of the things you are passing in as primitive values. Functional people would model things in terms of functions, OO people in terms of objects. Take your pick.
#Language? PHP is undeniably a great way to make web sites. I'm sure it's improved over the years, but few people have traditionally argued that PHP is an awesome general-purpose programming language. As I said, it looks like you are doing some fairly heavy lifting here. You might want to consider writing your API in a general purpose programming language that plays nicely with PHP.