hugo/common/predicate/predicate.go

// Copyright 2024 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 predicate

// P is a predicate function that tests whether a value of type T satisfies some condition.
type P[T any] func(T) bool

// And returns a predicate that is a short-circuiting logical AND of this and the given predicates.
func (p P[T]) And(ps ...P[T]) P[T] {
	return func(v T) bool {
		for _, pp := range ps {
			if !pp(v) {
				return false
			}
		}
		if p == nil {
			return true
		}
		return p(v)
	}
}

// Or returns a predicate that is a short-circuiting logical OR of this and the given predicates.
func (p P[T]) Or(ps ...P[T]) P[T] {
	return func(v T) bool {
		for _, pp := range ps {
			if pp(v) {
				return true
			}
		}
		if p == nil {
			return false
		}
		return p(v)
	}
}

// Negate returns a predicate that is a logical negation of this predicate.
func (p P[T]) Negate() P[T] {
	return func(v T) bool {
		return !p(v)
	}
}

// Filter returns a new slice holding only the elements of s that satisfy p.
// Filter modifies the contents of the slice s and returns the modified slice, which may have a smaller length.
func (p P[T]) Filter(s []T) []T {
	var n int
	for _, v := range s {
		if p(v) {
			s[n] = v
			n++
		}
	}
	return s[:n]
}

// FilterCopy returns a new slice holding only the elements of s that satisfy p.
func (p P[T]) FilterCopy(s []T) []T {
	var result []T
	for _, v := range s {
		if p(v) {
			result = append(result, v)
		}
	}
	return result
}