Forgive me if this is a basic question in FP. Let's consider Optional monad. I know I can use map to transform an Optional to another Optional based on a function (which will be called if optional has a value). But what if I have a function with two inputs, not one?
For example:
var data = Optional.of(100);
var result = data.map(x -> x * 2); //all good!
But what about:
int getData(Connection conn, int data) { ... }
var data = Optional.of(100);
var connection = getOptionalDataConnection();
var result = data.map(i -> getData(connection?, i)); //this does not work as the getData function only accepts non-optionals
I'm sure there is a term for this in FP world I'm just not familiar with it. But the idea is I have a map function which accepts "two" inputs, rather than one. And I want a helper/utility/... that will call my function if both inputs are there. But if any of them is "empty" should return Optional.empty().
What is this called and does Java support this?
What is this called and does Java support this?
This is called a monad, and yes, Java supports it via the flatMap function (monadic bind). Here demonstrated with just two optional integers:
var xo = Optional.of(100);
var yo = Optional.of(2);
var result = xo.flatMap(x -> yo.map(y -> x * y));
In this example, result is an Optional value holding the integer 200.
For the particular example in the OP, you actually don't need a monad, since using the capabilities of the Maybe/Optional applicative functor would be sufficient. I'm not well-versed in the Java ecosystem, however, and I don't see any apply-like methods in the API documentation. You could probably write it yourself, but my experience from Java's cousin language C# tells me that applicative functors are awkward in such languages.