Collections

In this section we'll explore ways to use Marcel Collections APIs enhancements

Literals

You can declare collections using the literal array syntax as shown below

List<int> ints = [1, 2, 3, 4]
List list = [1 new Object(), 1..2]


Set<char> chars = [`A`, `C`, `B`, `D`]

Operate on Collections and Arrays

Collections and Arrays have useful functions allowing you to operate on them

map

This operator allows you to map each element of the collection to another.

List<int> ints = [1, 2, 3]
List<float> floats = ints.mapToFloat { it + 1f } // mapping to another collection of primitive
int[] intArray = [3, 4, 5, 6]
List<int> otherInts = intArray.mapToInt { it - 1 }

List list = ints.map { new Foo(list) }
// specified type explicitely
List list2 = list.map { Foo foo -> foo.bar }

Note that for collections of primitive you don't have to specify explicitly your parameter's type. But for non-primitive lists, as Marcel doesn't support generic types, you'll have to explicitly declare your lambda's arguments.

find, findAll

The find operator finds and return the first element of the collection/array matching the provided predicate (or null if no element matched).

findAll returns a list of all elements matching the given predicate

Set<int> ints = [1, 2, 3]
int myInt = ints.find { it == 2 }
int[] intArray = [3, 4, 5, 6]
int myInt2 = intArray.find { it == 5 }
List<int> myInts = ints.findAll { it >= 2 }


List list = [1..1, 2..3, 3..4]
IntRange myRange = list.find { IntRange range -> range.contains(4) }
List myRanges = list.findAll { IntRange range -> range.contains(2) }

any, all, none

Those operations return booleans.

  • any returns true if at least one element of the collection/array matches the given predicate
  • all returns true if all elements of the collection/array matche the given predicate
  • none returns true if all elements of the collection/array does not match the given predicate