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58 lines
1.8 KiB
Go
58 lines
1.8 KiB
Go
// Copyright 2018 The Hugo Authors. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package collections
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import (
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"errors"
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"fmt"
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"reflect"
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)
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// Complement gives the elements in the last element of seqs that are not in
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// any of the others.
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// All elements of seqs must be slices or arrays of comparable types.
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//
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// The reasoning behind this rather clumsy API is so we can do this in the templates:
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// {{ $c := .Pages | complement $last4 }}
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func (ns *Namespace) Complement(seqs ...interface{}) (interface{}, error) {
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if len(seqs) < 2 {
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return nil, errors.New("complement needs at least two arguments")
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}
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universe := seqs[len(seqs)-1]
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as := seqs[:len(seqs)-1]
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aset, err := collectIdentities(as...)
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if err != nil {
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return nil, err
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}
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v := reflect.ValueOf(universe)
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switch v.Kind() {
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case reflect.Array, reflect.Slice:
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sl := reflect.MakeSlice(v.Type(), 0, 0)
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for i := 0; i < v.Len(); i++ {
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ev, _ := indirectInterface(v.Index(i))
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if !ev.Type().Comparable() {
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return nil, errors.New("elements in complement must be comparable")
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}
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if _, found := aset[normalize(ev)]; !found {
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sl = reflect.Append(sl, ev)
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}
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}
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return sl.Interface(), nil
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default:
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return nil, fmt.Errorf("arguments to complement must be slices or arrays")
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}
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}
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