Add SliceFrom/To mapper operations

pkg/mapper/mapper.go

@@ -248,3 +248,24 @@ func Decrement[E constraint.RealNumber](step E) func(E) E {
 		return e - step
 	}
 }
+
+// SliceFrom returns a function that accepts a slice of any type E and returns a slice of the same type containing all elements from the provided `start` index to the end of the slice.
+func SliceFrom[E any](start int) func([]E) []E {
+	return func(s []E) []E {
+		return s[start:]
+	}
+}
+
+// SliceTo returns a function that accepts a slice of any type E and returns a slice of the same type containing all elements from the start of the slice up to, but excluding, the provided `end` index.
+func SliceTo[E any](end int) func([]E) []E {
+	return func(s []E) []E {
+		return s[:end]
+	}
+}
+
+// SliceFromTo returns a function that accepts a slice of any type E and returns a slice of the same type containing all elements from the provided `start` index up to, but excluding, the provided `end` index.
+func SliceFromTo[E any](start int, end int) func([]E) []E {
+	return func(s []E) []E {
+		return s[start:end]
+	}
+}

pkg/mapper/mapper_test.go

@@ -1,6 +1,7 @@
 package mapper
 
 import (
+	"slices"
 	"testing"
 
 	"github.com/jpfourny/papaya/pkg/pointer"
@@ -473,3 +474,30 @@ func TestDecrement(t *testing.T) {
 		t.Errorf("Decrement(2)(42) = %#v; want %#v", got, want)
 	}
 }
+
+func TestSliceFrom(t *testing.T) {
+	m := SliceFrom[int](1)
+	got := m([]int{1, 2, 3})
+	want := []int{2, 3}
+	if !slices.Equal(got, want) {
+		t.Errorf("SliceFrom(1)([1, 2, 3]) = %#v; want %#v", got, want)
+	}
+}
+
+func TestSliceTo(t *testing.T) {
+	m := SliceTo[int](2)
+	got := m([]int{1, 2, 3})
+	want := []int{1, 2}
+	if !slices.Equal(got, want) {
+		t.Errorf("SliceTo(2)([1, 2, 3]) = %#v; want %#v", got, want)
+	}
+}
+
+func TestSliceFromTo(t *testing.T) {
+	m := SliceFromTo[int](1, 2)
+	got := m([]int{1, 2, 3})
+	want := []int{2}
+	if !slices.Equal(got, want) {
+		t.Errorf("SliceFromTo(1, 2)([1, 2, 3]) = %#v; want %#v", got, want)
+	}
+}