Add iterator functions

go.mod

@@ -1,3 +1,5 @@
 module github.com/isgj/collection
 
 go 1.18
+
+require golang.org/x/exp v0.0.0-20220321173239-a90fa8a75705 // indirect

go.sum

@@ -0,0 +1,2 @@
+golang.org/x/exp v0.0.0-20220321173239-a90fa8a75705 h1:ba9YlqfDGTTQ5aZ2fwOoQ1hf32QySyQkR6ODGDzHlnE=
+golang.org/x/exp v0.0.0-20220321173239-a90fa8a75705/go.mod h1:lgLbSvA5ygNOMpwM/9anMpWVlVJ7Z+cHWq/eFuinpGE=

iter/iterators.go

@@ -0,0 +1,67 @@
+// Utility iterator functions.
+package iter
+
+import (
+	c "github.com/isgj/collection"
+	"golang.org/x/exp/constraints"
+)
+
+// Map will map values of type `I` from to type `O` through the `to` mapper function.
+//
+// Example:
+// 		v := collection.Vec[int]{1, 2, 3, 4, 5, 6, 7, 8, 9}
+// 		number_iterator := v.Iter().Filter(func(item int) string { return item%2 == 0})
+// 		iter.Map(number_iterator, func(item int) string { return fmt.Sprint("number ", item) }).
+// 			ForEach(func(item string) { fmt.Prinln(item) })
+//
+// This is a workaround to implement `Map` as currently methods cannot have type paramters.
+func Map[I any, O any](it c.Iterator[I], to func(item I) O) c.Iterator[O] {
+	return func() (O, bool) {
+		if i, ok := it(); ok {
+			return to(i), true
+		}
+		return *new(O), false
+	}
+}
+
+// Reduce will reduce the values through the reducer
+//
+// This is a workaround to implement `Reduce` as currently methods cannot have type paramters.
+func Reduce[I any, O any](it c.Iterator[I], start O, reducer func(acc O, item I) O) O {
+	for i, ok := it(); ok; i, ok = it() {
+		start = reducer(start, i)
+	}
+	return start
+}
+
+// Sum will return the sum of the values. If the iterated values are strings it will concatenate them
+func Sum[T constraints.Ordered](it c.Iterator[T]) T {
+	result, _ := it()
+	for i, ok := it(); ok; i, ok = it() {
+		result += i
+	}
+	return result
+}
+
+func FromSlice[T any](s []T) c.Iterator[T] {
+	return c.Vec[T](s).Iter()
+}
+
+// Iterate from 0 to `end` by steps of 1
+func Range(end int) c.Iterator[int] {
+	return XRange(0, end, 1)
+}
+
+// Iterate from `start` to `end` by steps of `step`.
+// Currently the range will only increase, the step will be added for each iteration so make sure that it will
+// eventually reach the end, otherwise you enter an infinite loop.
+func XRange(start, end, step int) c.Iterator[int] {
+	return func() (int, bool) {
+		if start < end {
+			r := start
+			start += step
+			return r, true
+		}
+		return 0, false
+	}
+}