The absence of tuples in Java is often bemoaned. Tuples are collections of a variety of types. They might look like (“benji”,8,”weber”) – a 3-tuple of a string, a number, and another string. People often wish to use tuples to return more than one value from a method.<\/p>\n
Often this is a smell that we need to create a domain type that is more meaningful than a tuple, but in some cases tuples are actually the best tool for the job.<\/p>\n
We can pretty easily create our own tuple types, and now that we have Lambdas we can consume them pretty easily as well. There is a little unnecessary verbosity left over from type signatures, but we can avoid it in most cases.<\/p>\n
If we want to return a tuple from a method, by statically importing an “tuple” method that is overloaded for each arity of tuple we can do<\/p>\n
\r\nstatic TriTuple me() {\r\n return tuple(\"benji\",9001,\"weber\");\r\n}\r\n<\/pre>\nOther than the return type of the method it is fairly concise.<\/p>\n
On the consuming side it would be nice to be able to use helpful names for each field in the tuple, rather than the ._1() or .one() accessors that are used in many tuple implementations.<\/p>\n
This is easily realised thanks to lambdas. We can simply define a map method on the tuple that accepts a function with the same arity of the tuple, to transform the tuple into something else.<\/p>\n
Using the above method now becomes<\/p>\n
\r\nString name = me()\r\n .map((firstname, favouriteNo, surname) -> firstname + \" \" + surname);\r\n\r\nassertEquals(\"benji weber\", name);\r\n<\/pre>\nWe can even throw checked exceptions on the consuming side if we allow our map method to accept functions that throw exceptions.<\/p>\n
\r\nString name = me()\r\n .map((firstname, favouriteNo, surname) -> {\r\n if (favouriteNo > 9000) throw new NumberTooBigException();\r\n return firstname;\r\n });\r\n<\/pre>\nOf course we’d also like identical tuples to be equal to each other so that this is true.<\/p>\n
\r\nassertEquals(tuple(\"hello\",\"world\"), tuple(\"hello\", \"world\"));\r\n<\/pre>\nThe implementation looks like this, re-using the value-object pattern I described previously<\/a><\/p>\n\r\npublic interface Tuple {\r\n \/\/...\r\n static TriTuple tuple(A a, B b, C c) {\r\n return TriTuple.of(a, b, c);\r\n }\r\n \/\/...\r\n}\r\n\r\npublic interface TriTuple {\r\n A one();\r\n B two();\r\n C three();\r\n static TriTuple of(A a, B b, C c) {\r\n abstract class TriTupleValue extends Value> implements TriTuple {}\r\n return new TriTupleValue() {\r\n public A one() { return a; }\r\n public B two() { return b; }\r\n public C three() { return c; }\r\n }.using(TriTuple::one, TriTuple::two, TriTuple::three);\r\n }\r\n\r\n default R map(ExceptionalTriFunction f) throws E {\r\n return f.apply(one(),two(),three());\r\n }\r\n\r\n default void consume(ExceptionalTriConsumer consumer) throws E {\r\n consumer.accept(one(), two(), three());\r\n }\r\n}\r\n<\/pre>\nBrowse the full code on Github<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"The absence of tuples in Java is often bemoaned. Tuples are collections of a variety of types. They might look like (“benji”,8,”weber”) – a 3-tuple of a string, a number, and another string. People often wish to use tuples to return more than one value from a method. Often this is a smell that we… Read more »<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[8],"tags":[],"yoast_head":"\n\n\n\n\n\n\n\n\n\n\n