Merge pull request #82 from meian/21-last-implements

#21 last implements

last.go

@@ -0,0 +1,60 @@
+package gcf
+
+type lastIterable[T any] struct {
+	itb   Iterable[T]
+	count int
+}
+
+type lastIterator[T any] struct {
+	it      Iterator[T]
+	count   int
+	i       int
+	built   bool
+	current T
+}
+
+// Last makes Iterable with count elements from end.
+//
+//   itb := gcf.FromSlice([]{1, 2, 3})
+//   itb = gcf.Last(itb, 2)
+//
+// If count is 0 or negative, returns empty Iterable.
+func Last[T any](itb Iterable[T], count int) Iterable[T] {
+	if isEmpty(itb) {
+		return orEmpty(itb)
+	}
+	if count < 1 {
+		return empty[T]()
+	}
+	return &lastIterable[T]{itb, count}
+}
+
+func (itb *lastIterable[T]) Iterator() Iterator[T] {
+	return &lastIterator[T]{itb.itb.Iterator(), itb.count, 0, false, zero[T]()}
+}
+
+func (it *lastIterator[T]) MoveNext() bool {
+	if !it.built {
+		it.build()
+	}
+	if !it.it.MoveNext() {
+		it.current = zero[T]()
+		return false
+	}
+	it.current = it.it.Current()
+	return true
+}
+
+func (it *lastIterator[T]) Current() T {
+	return it.current
+}
+
+func (it *lastIterator[T]) build() {
+	s := iteratorToSlice(it.it)
+	if len(s) <= it.count {
+		it.it = makeSliceIterator(s)
+	} else {
+		it.it = makeSliceIterator(s[len(s)-it.count:])
+	}
+	it.built = true
+}

last_test.go

@@ -0,0 +1,101 @@
+package gcf_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/meian/gcf"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLast(t *testing.T) {
+	type args struct {
+		itb   gcf.Iterable[int]
+		count int
+	}
+	tests := []struct {
+		name string
+		args args
+		want []int
+	}{
+		{
+			name: "last 1 from slice 3",
+			args: args{
+				itb:   gcf.FromSlice([]int{1, 2, 3}),
+				count: 1,
+			},
+			want: []int{3},
+		},
+		{
+			name: "last 2 from slice 3",
+			args: args{
+				itb:   gcf.FromSlice([]int{1, 2, 3}),
+				count: 2,
+			},
+			want: []int{2, 3},
+		},
+		{
+			name: "last 3 from slice 3",
+			args: args{
+				itb:   gcf.FromSlice([]int{1, 2, 3}),
+				count: 3,
+			},
+			want: []int{1, 2, 3},
+		},
+		{
+			name: "last 4 from slice 3",
+			args: args{
+				itb:   gcf.FromSlice([]int{1, 2, 3}),
+				count: 4,
+			},
+			want: []int{1, 2, 3},
+		},
+		{
+			name: "last 0 from slice 3",
+			args: args{
+				itb:   gcf.FromSlice([]int{1, 2, 3}),
+				count: 0,
+			},
+			want: []int{},
+		},
+		{
+			name: "last negative",
+			args: args{
+				itb:   gcf.FromSlice([]int{1, 2, 3}),
+				count: -1,
+			},
+			want: []int{},
+		},
+		{
+			name: "nil Iterable",
+			args: args{
+				itb:   nil,
+				count: 3,
+			},
+			want: []int{},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			itb := gcf.Last(tt.args.itb, tt.args.count)
+			s := gcf.ToSlice(itb)
+			assert.Equal(t, tt.want, s)
+		})
+	}
+
+	itb := gcf.FromSlice([]int{1, 2, 3})
+	itb = gcf.Last(itb, 2)
+	testBeforeAndAfter(t, itb)
+
+	testEmptyChain(t, func(itb gcf.Iterable[int]) gcf.Iterable[int] {
+		return gcf.Last(itb, 2)
+	})
+}
+
+func ExampleLast() {
+	itb := gcf.FromSlice([]int{1, 2, 3, 4, 5})
+	itb = gcf.Last(itb, 3)
+	fmt.Println(gcf.ToSlice(itb))
+	// Output:
+	// [3 4 5]
+}