complement.go (1675B)
1 // Copyright 2018 The Hugo Authors. All rights reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 // http://www.apache.org/licenses/LICENSE-2.0
7 //
8 // Unless required by applicable law or agreed to in writing, software
9 // distributed under the License is distributed on an "AS IS" BASIS,
10 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11 // See the License for the specific language governing permissions and
12 // limitations under the License.
13
14 package collections
15
16 import (
17 "errors"
18 "fmt"
19 "reflect"
20 )
21
22 // Complement gives the elements in the last element of seqs that are not in
23 // any of the others.
24 // All elements of seqs must be slices or arrays of comparable types.
25 //
26 // The reasoning behind this rather clumsy API is so we can do this in the templates:
27 // {{ $c := .Pages | complement $last4 }}
28 func (ns *Namespace) Complement(seqs ...any) (any, error) {
29 if len(seqs) < 2 {
30 return nil, errors.New("complement needs at least two arguments")
31 }
32
33 universe := seqs[len(seqs)-1]
34 as := seqs[:len(seqs)-1]
35
36 aset, err := collectIdentities(as...)
37 if err != nil {
38 return nil, err
39 }
40
41 v := reflect.ValueOf(universe)
42 switch v.Kind() {
43 case reflect.Array, reflect.Slice:
44 sl := reflect.MakeSlice(v.Type(), 0, 0)
45 for i := 0; i < v.Len(); i++ {
46 ev, _ := indirectInterface(v.Index(i))
47 if _, found := aset[normalize(ev)]; !found {
48 sl = reflect.Append(sl, ev)
49 }
50 }
51 return sl.Interface(), nil
52 default:
53 return nil, fmt.Errorf("arguments to complement must be slices or arrays")
54 }
55 }