Add Component.identity

CHANGES.md

@@ -1,3 +1,9 @@
+Unreleased
+--------------
+
+- archi: add `Component.identity`which creates a component whose value is its
+  argument ([#11](https://github.com/anmonteiro/archi/pull/11))
+
 0.1.0 2020-05-07
 --------------
 

lib/archi.ml

@@ -207,6 +207,12 @@ module Make (Io : IO) = struct
      fun ~start ~stop ->
       Component { start; stop; hkey = Hmap.Key.create (); dependencies = [] }
 
+    let identity : type ctx ty. ty -> (ctx, ty) t =
+     fun c ->
+      let start _ctx = Io.Result.return c in
+      let stop _c = Io.return () in
+      make ~start ~stop
+
     let make_m
         : type ctx a.
           (module SIMPLE_COMPONENT with type t = a and type ctx = ctx)

lib/archi_intf.ml

@@ -82,6 +82,8 @@ module type S = sig
 
     (** Creating components *)
 
+    val identity : 'ty -> ('ctx, 'ty) t
+
     val make
       :  start:('ctx -> ('a, string) result Io.t)
       -> stop:('a -> unit Io.t)

nix/sources.nix

@@ -3,7 +3,7 @@
 let
   overlays =
     builtins.fetchTarball
-      https://github.com/anmonteiro/nix-overlays/archive/3ce96cd.tar.gz;
+      https://github.com/anmonteiro/nix-overlays/archive/0e67e7b.tar.gz;
 
 in
 

test/test.ml

@@ -190,6 +190,39 @@ let test_get () =
   | Error error ->
     Alcotest.fail error
 
+let test_identity () =
+  let identity_component = Component.identity "I'm the component" in
+  let system =
+    System.make_reusable
+      ~lift:(fun id -> id)
+      [ "identity component", identity_component ]
+  in
+  let started = System.start () system in
+  (match started with
+  | Ok system ->
+    let id = System.get system in
+    Alcotest.(check string "expected value" "I'm the component" id)
+  | Error error ->
+    Alcotest.fail error);
+  let v = ref "" in
+  let server =
+    Component.using
+      ~dependencies:[ identity_component ]
+      ~start:(fun () id ->
+        v := id;
+        Ok ())
+      ~stop:(fun _ -> ())
+  in
+  let system =
+    System.make [ "identity component", identity_component; "server", server ]
+  in
+  let started = System.start () system in
+  match started with
+  | Ok _system ->
+    Alcotest.(check string "expected value" "I'm the component" !v)
+  | Error error ->
+    Alcotest.fail error
+
 let suite =
   [ "start / stop order", `Quick, test_start_stop_order system
   ; ( "start / stop order, module system"
@@ -198,6 +231,7 @@ let suite =
   ; "duplicates", `Quick, test_duplicates_start_once
   ; "system depending on system", `Quick, test_start_stop_order_system_deps
   ; "get resulting value", `Quick, test_get
+  ; "test identity component", `Quick, test_identity
   ]
 
 let () = Alcotest.run "archi unit tests" [ "archi", suite ]