From 58aa302f49311475cce11dcbd477df217e790ea6 Mon Sep 17 00:00:00 2001
From: Joel Stålnacke <joel@saker.fi>
Date: Fri, 13 Feb 2026 20:48:51 +0200
Subject: Initial commit

---
 ...onalObjects.Examples.DependencyInjection.fsproj | 16 +++++++
 examples/DependencyInjection/Program.fs            | 51 ++++++++++++++++++++++
 2 files changed, 67 insertions(+)
 create mode 100644 examples/DependencyInjection/FunctionalObjects.Examples.DependencyInjection.fsproj
 create mode 100644 examples/DependencyInjection/Program.fs

(limited to 'examples/DependencyInjection')

diff --git a/examples/DependencyInjection/FunctionalObjects.Examples.DependencyInjection.fsproj b/examples/DependencyInjection/FunctionalObjects.Examples.DependencyInjection.fsproj
new file mode 100644
index 0000000..806da26
--- /dev/null
+++ b/examples/DependencyInjection/FunctionalObjects.Examples.DependencyInjection.fsproj
@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\FunctionalObjects\FunctionalObjects.fsproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/examples/DependencyInjection/Program.fs b/examples/DependencyInjection/Program.fs
new file mode 100644
index 0000000..84b51c6
--- /dev/null
+++ b/examples/DependencyInjection/Program.fs
@@ -0,0 +1,51 @@
+open System
+
+type Logger = {
+    Log : string -> unit
+}
+
+type HelloService = {
+    SayHelloTo : string -> unit
+}
+
+// This is the constructor of a logger that adds a timestamp in the specified
+// format to each log message it writes.
+let dateTimeLogger (dateFormat : string) =
+    { Log =
+        fun msg ->
+            let timestamp = DateTime.Now.ToString dateFormat
+            printfn "[%s]: %s" timestamp msg }
+
+let logger = dateTimeLogger "yyyy-MM-dd hh:mm:ss"
+
+// This implementation of Logger ignores all messages
+let noopLogger =
+    { Log = ignore }
+
+let doSomething logger =
+    logger.Log "Starting to do something"
+    let x = 1 + 1
+    sprintf "Did something! Result: %d" x
+    |> logger.Log
+
+// Implementations can be injected to application code
+doSomething logger
+doSomething noopLogger
+
+// Implement HelloService. Our implementation depends on a Logger to write
+// messages to.
+let helloService logger =
+    { SayHelloTo =
+        fun user ->
+            sprintf "Saying hi to %s" user
+            |> logger.Log
+            printfn "Hi %s!" user
+            logger.Log "Operation complete" }
+
+// Create an instance of helloService.
+//
+// We don't want to do anything with the messages so we discard them by using
+// injecting noopLogger as the implementation of Logger.
+let instance = helloService noopLogger
+
+instance.SayHelloTo "John"
-- 
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