reflect: add Append and AppendSlice functions.

R=r, nigeltao_gnome, rog, niemeyer
CC=golang-dev
https://golang.org/cl/3529042

2 files changed, 94 insertions, 1 deletions

diff --git a/src/pkg/reflect/all_test.go b/src/pkg/reflect/all_test.go
index aa831f3365..1652e17316 100644
--- a/src/pkg/reflect/all_test.go
+++ b/src/pkg/reflect/all_test.go
@@ -498,7 +498,54 @@ func TestFunctionValue(t *testing.T) {
 	assert(t, v.Type().String(), "func()")
 }
 
-func TestCopyArray(t *testing.T) {
+var appendTests = []struct {
+	orig, extra []int
+}{
+	{make([]int, 2, 4), []int{22}},
+	{make([]int, 2, 4), []int{22, 33, 44}},
+}
+
+func TestAppend(t *testing.T) {
+	for i, test := range appendTests {
+		origLen, extraLen := len(test.orig), len(test.extra)
+		want := append(test.orig, test.extra...)
+		// Convert extra from []int to []Value.
+		e0 := make([]Value, len(test.extra))
+		for j, e := range test.extra {
+			e0[j] = NewValue(e)
+		}
+		// Convert extra from []int to *SliceValue.
+		e1 := NewValue(test.extra).(*SliceValue)
+		// Test Append.
+		a0 := NewValue(test.orig).(*SliceValue)
+		have0 := Append(a0, e0...).Interface().([]int)
+		if !DeepEqual(have0, want) {
+			t.Errorf("Append #%d: have %v, want %v", i, have0, want)
+		}
+		// Check that the orig and extra slices were not modified.
+		if len(test.orig) != origLen {
+			t.Errorf("Append #%d origLen: have %v, want %v", i, len(test.orig), origLen)
+		}
+		if len(test.extra) != extraLen {
+			t.Errorf("Append #%d extraLen: have %v, want %v", i, len(test.extra), extraLen)
+		}
+		// Test AppendSlice.
+		a1 := NewValue(test.orig).(*SliceValue)
+		have1 := AppendSlice(a1, e1).Interface().([]int)
+		if !DeepEqual(have1, want) {
+			t.Errorf("AppendSlice #%d: have %v, want %v", i, have1, want)
+		}
+		// Check that the orig and extra slices were not modified.
+		if len(test.orig) != origLen {
+			t.Errorf("AppendSlice #%d origLen: have %v, want %v", i, len(test.orig), origLen)
+		}
+		if len(test.extra) != extraLen {
+			t.Errorf("AppendSlice #%d extraLen: have %v, want %v", i, len(test.extra), extraLen)
+		}
+	}
+}
+
+func TestCopy(t *testing.T) {
 	a := []int{1, 2, 3, 4, 10, 9, 8, 7}
 	b := []int{11, 22, 33, 44, 1010, 99, 88, 77, 66, 55, 44}
 	c := []int{11, 22, 33, 44, 1010, 99, 88, 77, 66, 55, 44}
diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index 8b2c1a9530..e0bcb1a39d 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -400,6 +400,52 @@ type ArrayOrSliceValue interface {
 	addr() addr
 }
 
+// grow grows the slice s so that it can hold extra more values, allocating
+// more capacity if needed. It also returns the old and new slice lengths.
+func grow(s *SliceValue, extra int) (*SliceValue, int, int) {
+	i0 := s.Len()
+	i1 := i0 + extra
+	if i1 < i0 {
+		panic("append: slice overflow")
+	}
+	m := s.Cap()
+	if i1 <= m {
+		return s.Slice(0, i1), i0, i1
+	}
+	if m == 0 {
+		m = extra
+	} else {
+		for m < i1 {
+			if i0 < 1024 {
+				m += m
+			} else {
+				m += m / 4
+			}
+		}
+	}
+	t := MakeSlice(s.Type().(*SliceType), i1, m)
+	Copy(t, s)
+	return t, i0, i1
+}
+
+// Append appends the values x to a slice s and returns the resulting slice.
+// Each x must have the same type as s' element type.
+func Append(s *SliceValue, x ...Value) *SliceValue {
+	s, i0, i1 := grow(s, len(x))
+	for i, j := i0, 0; i < i1; i, j = i+1, j+1 {
+		s.Elem(i).SetValue(x[j])
+	}
+	return s
+}
+
+// AppendSlice appends a slice t to a slice s and returns the resulting slice.
+// The slices s and t must have the same element type.
+func AppendSlice(s, t *SliceValue) *SliceValue {
+	s, i0, i1 := grow(s, t.Len())
+	Copy(s.Slice(i0, i1), t)
+	return s
+}
+
 // Copy copies the contents of src into dst until either
 // dst has been filled or src has been exhausted.
 // It returns the number of elements copied.