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53 lines
1.8 KiB
Go
53 lines
1.8 KiB
Go
// Copyright (c) 2023 - 2025 IBM Corp.
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// 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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//
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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 predicate
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import (
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F "github.com/IBM/fp-go/v2/function"
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)
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// ContraMap creates a new predicate by transforming the input before applying an existing predicate.
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//
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// This is a contravariant functor operation that allows you to adapt a predicate for type A
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// to work with type B by providing a function that converts B to A. The resulting predicate
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// first applies the mapping function f to transform the input, then applies the original predicate.
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//
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// This is particularly useful when you have a predicate for one type and want to reuse it
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// for a related type without rewriting the predicate logic.
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//
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// Parameters:
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// - f: A function that converts values of type B to type A
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//
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// Returns:
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// - An Operator that transforms a Predicate[A] into a Predicate[B]
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//
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// Example:
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//
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// type Person struct { Age int }
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// isAdult := func(age int) bool { return age >= 18 }
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// getAge := func(p Person) int { return p.Age }
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// isPersonAdult := F.Pipe1(isAdult, ContraMap(getAge))
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// isPersonAdult(Person{Age: 25}) // true
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// isPersonAdult(Person{Age: 15}) // false
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func ContraMap[A, B any](f func(B) A) Operator[A, B] {
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return func(pred Predicate[A]) Predicate[B] {
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return F.Flow2(
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f,
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pred,
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)
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}
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}
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