fix: add more examples

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

option/examples_extract_test.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2023 IBM Corp.
+// 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 option
+
+import (
+	"fmt"
+
+	F "github.com/IBM/fp-go/function"
+	N "github.com/IBM/fp-go/number"
+)
+
+func ExampleOption_extraction() {
+
+	noneValue := None[int]()
+	someValue := Of(42)
+
+	// Convert Option[T] to T
+	fromNone, okFromNone := Unwrap(noneValue) // 0, false
+	fromSome, okFromSome := Unwrap(someValue) // 42, true
+
+	// Convert Option[T] with a default value
+	noneWithDefault := GetOrElse(F.Constant(0))(noneValue) // 0
+	someWithDefault := GetOrElse(F.Constant(0))(someValue) // 42
+
+	// Apply a different function on None/Some(...)
+	doubleOrZero := Fold(
+		F.Constant(0), // none case
+		N.Mul(2),      // some case
+	) // func(ma Option[int]) int
+
+	doubleFromNone := doubleOrZero(noneValue) // 0
+	doubleFromSome := doubleOrZero(someValue) // 84
+
+	// Pro-tip: Fold is short for the following:
+	doubleOfZeroBis := F.Flow2(
+		Map(N.Mul(2)),            // some case
+		GetOrElse(F.Constant(0)), // none case
+	)
+	doubleFromNoneBis := doubleOfZeroBis(noneValue) // 0
+	doubleFromSomeBis := doubleOfZeroBis(someValue) // 84
+
+	fmt.Printf("%d, %t\n", fromNone, okFromNone)
+	fmt.Printf("%d, %t\n", fromSome, okFromSome)
+	fmt.Println(noneWithDefault)
+	fmt.Println(someWithDefault)
+	fmt.Println(doubleFromNone)
+	fmt.Println(doubleFromSome)
+	fmt.Println(doubleFromNoneBis)
+	fmt.Println(doubleFromSomeBis)
+
+	// Output:
+	// 0, false
+	// 42, true
+	// 0
+	// 42
+	// 0
+	// 84
+	// 0
+	// 84
+}