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// Copyright 2019 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package collections
import (
"fmt"
"reflect"
)
// Append appends from to a slice to and returns the resulting slice.
// If length of from is one and the only element is a slice of same type as to,
// it will be appended.
func Append(to any, from ...any) (any, error) {
if len(from) == 0 {
return to, nil
}
tov, toIsNil := indirect(reflect.ValueOf(to))
toIsNil = toIsNil || to == nil
var tot reflect.Type
if !toIsNil {
if tov.Kind() == reflect.Slice {
// Create a copy of tov, so we don't modify the original.
c := reflect.MakeSlice(tov.Type(), tov.Len(), tov.Len()+len(from))
reflect.Copy(c, tov)
tov = c
}
if tov.Kind() != reflect.Slice {
return nil, fmt.Errorf("expected a slice, got %T", to)
}
tot = tov.Type().Elem()
if tot.Kind() == reflect.Slice {
totvt := tot.Elem()
fromvs := make([]reflect.Value, len(from))
for i, f := range from {
fromv := reflect.ValueOf(f)
fromt := fromv.Type()
if fromt.Kind() == reflect.Slice {
fromt = fromt.Elem()
}
if totvt != fromt {
return nil, fmt.Errorf("cannot append slice of %s to slice of %s", fromt, totvt)
} else {
fromvs[i] = fromv
}
}
return reflect.Append(tov, fromvs...).Interface(), nil
}
toIsNil = tov.Len() == 0
if len(from) == 1 {
fromv := reflect.ValueOf(from[0])
if !fromv.IsValid() {
// from[0] is nil
return appendToInterfaceSliceFromValues(tov, fromv)
}
fromt := fromv.Type()
if fromt.Kind() == reflect.Slice {
fromt = fromt.Elem()
}
if fromv.Kind() == reflect.Slice {
if toIsNil {
// If we get nil []string, we just return the []string
return from[0], nil
}
// If we get []string []string, we append the from slice to to
if tot == fromt {
return reflect.AppendSlice(tov, fromv).Interface(), nil
} else if !fromt.AssignableTo(tot) {
// Fall back to a []interface{} slice.
return appendToInterfaceSliceFromValues(tov, fromv)
}
}
}
}
if toIsNil {
return Slice(from...), nil
}
for _, f := range from {
fv := reflect.ValueOf(f)
if !fv.IsValid() || !fv.Type().AssignableTo(tot) {
// Fall back to a []interface{} slice.
tov, _ := indirect(reflect.ValueOf(to))
return appendToInterfaceSlice(tov, from...)
}
tov = reflect.Append(tov, fv)
}
return tov.Interface(), nil
}
func appendToInterfaceSliceFromValues(slice1, slice2 reflect.Value) ([]any, error) {
var tos []any
for _, slice := range []reflect.Value{slice1, slice2} {
if !slice.IsValid() {
tos = append(tos, nil)
continue
}
for i := 0; i < slice.Len(); i++ {
tos = append(tos, slice.Index(i).Interface())
}
}
return tos, nil
}
func appendToInterfaceSlice(tov reflect.Value, from ...any) ([]any, error) {
var tos []any
for i := 0; i < tov.Len(); i++ {
tos = append(tos, tov.Index(i).Interface())
}
tos = append(tos, from...)
return tos, nil
}
// indirect is borrowed from the Go stdlib: 'text/template/exec.go'
// TODO(bep) consolidate
func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
for ; v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface; v = v.Elem() {
if v.IsNil() {
return v, true
}
if v.Kind() == reflect.Interface && v.NumMethod() > 0 {
break
}
}
return v, false
}
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