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// Copyright 2018 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 (
"errors"
"fmt"
"reflect"
)
// Complement gives the elements in the last element of seqs that are not in
// any of the others.
// All elements of seqs must be slices or arrays of comparable types.
//
// The reasoning behind this rather clumsy API is so we can do this in the templates:
// {{ $c := .Pages | complement $last4 }}
func (ns *Namespace) Complement(seqs ...any) (any, error) {
if len(seqs) < 2 {
return nil, errors.New("complement needs at least two arguments")
}
universe := seqs[len(seqs)-1]
as := seqs[:len(seqs)-1]
aset, err := collectIdentities(as...)
if err != nil {
return nil, err
}
v := reflect.ValueOf(universe)
switch v.Kind() {
case reflect.Array, reflect.Slice:
sl := reflect.MakeSlice(v.Type(), 0, 0)
for i := 0; i < v.Len(); i++ {
ev, _ := indirectInterface(v.Index(i))
if _, found := aset[normalize(ev)]; !found {
sl = reflect.Append(sl, ev)
}
}
return sl.Interface(), nil
default:
return nil, fmt.Errorf("arguments to complement must be slices or arrays")
}
}
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