Dependency injection (#81)

* fix: checkin

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

* fix: add initial DI implementation

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

* fix: add multi provider

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

* fix: simplify DI implementation

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

* fix: simplify provider

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

* fix: add Switch to function package

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

* fix: add DI

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

---------

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

di/erasure/token.go

@@ -0,0 +1,45 @@
+// 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 erasure
+
+import (
+	"fmt"
+
+	O "github.com/IBM/fp-go/option"
+)
+
+const (
+	BehaviourMask = 0x0f
+	Identity      = 0 // required dependency
+	Option        = 1 // optional dependency
+	IOEither      = 2 // lazy and required
+	IOOption      = 3 // lazy and optional
+
+	TypeMask = 0xf0
+	Multi    = 1 << 4 // array of implementations
+	Item     = 2 << 4 // item of a multi token
+)
+
+// Dependency describes the relationship to a service
+type Dependency interface {
+	fmt.Stringer
+	// Id returns a unique identifier for a token that can be used as a cache key
+	Id() string
+	// Flag returns a tag that identifies the behaviour of the dependency
+	Flag() int
+	// ProviderFactory optionally returns an attached [ProviderFactory] that represents the default for this dependency
+	ProviderFactory() O.Option[ProviderFactory]
+}