Let's say I have a method that applies multiple functions to a value.
Example usage:
String value = "a string with numb3r5";
Function<String, List<String>> fn1 = ...
Function<List<String>, String> fn2 = ...
Function<String, List<Integer>> fn3 = ...
InputConverter<String> converter = new InputConverter<>(value);
List<Integer> ints = converter.convertBy(fn1, fn2, fn3);
Is it possible to make it apply multiple functions with various inputs and return values?
I've tried using wildcards, but this doesn't work.
public class InputConverter<T> {
private final T src;
public InputConverter(T src) {
this.src = src;
}
public <R> R convertBy(Function<?, ?>... functions) {
R value = (R) src;
for (Function<?, ?> function : functions)
value = (R) function.apply(value);
^^^^^
return value;
}
}
You can use a chain on Function
like the following
Function<String, List<Integer>> functionChain = fn1.andThen(fn2).andThen(fn3);
You can achieve nearly the same thing by using raw types
@SuppressWarnings({"unchecked", "rawtypes"})
public <R> R convertBy(Function... functions) {
Function functionsChain = Function.identity();
for (Function function : functions) {
functionsChain = functionsChain.andThen(function);
}
return (R) functionsChain.apply(src);
}
Otherwise, the only other I see is to use the same pattern as Optional
or Stream
like suggested in the comments
List<Integer> fileInputStreams = converter.convertBy(fn1)
.convertBy(fn2)
.convertBy(fn3)
.get();
// with this implementation
public static class InputConverter<T> {
private final T src;
public InputConverter(T src) {
this.src = src;
}
public <R> InputConverter<R> convertBy(Function<T, R> function) {
return new InputConverter<>(function.apply(src));
}
public T get() {
return src;
}
}