From 7d641d5f1fe4e8a83fd078952431bb8ae30b3443 Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Mon, 1 Oct 2018 14:04:50 +0200
Subject: [PATCH] base: add Reconstructible::conditional method

The new 'conditional' method simplifies the typical use case for
'Constructible' objects where the constructed/destructed state depends
on a configuration parameter. The method alleviates the need to
re-implement the logic again and again.

The patch also removes the 'Reconstructible' constructor arguments
because they are unused.

Fixes #3006
---
 repos/base-hw/src/bootstrap/platform.cc   |  1 -
 repos/base-hw/src/bootstrap/platform.h    |  2 +-
 repos/base/include/util/reconstructible.h | 20 +++++++++++++++-----
 repos/gems/src/app/depot_query/main.cc    |  8 ++++----
 4 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/repos/base-hw/src/bootstrap/platform.cc b/repos/base-hw/src/bootstrap/platform.cc
index 211b8b98a..4fc5fdf12 100644
--- a/repos/base-hw/src/bootstrap/platform.cc
+++ b/repos/base-hw/src/bootstrap/platform.cc
@@ -163,7 +163,6 @@ static constexpr Genode::Boot_modules_header & header() {
 Platform::Platform()
 : bootstrap_region((addr_t)&_prog_img_beg,
                    ((addr_t)&_prog_img_end - (addr_t)&_prog_img_beg)),
-  core_pd(ram_alloc),
   core_elf_addr(header().base),
   core_elf(core_elf_addr)
 {
diff --git a/repos/base-hw/src/bootstrap/platform.h b/repos/base-hw/src/bootstrap/platform.h
index 18b814190..8ce41c450 100644
--- a/repos/base-hw/src/bootstrap/platform.h
+++ b/repos/base-hw/src/bootstrap/platform.h
@@ -127,7 +127,7 @@ class Bootstrap::Platform
 		Bootstrap::Pic            pic       { };
 		Ram_allocator             ram_alloc { };
 		Memory_region const       bootstrap_region;
-		Genode::Constructible<Pd> core_pd;
+		Genode::Constructible<Pd> core_pd { };
 		addr_t                    core_elf_addr;
 		Elf                       core_elf;
 
diff --git a/repos/base/include/util/reconstructible.h b/repos/base/include/util/reconstructible.h
index 771ff09b3..1dc413e34 100644
--- a/repos/base/include/util/reconstructible.h
+++ b/repos/base/include/util/reconstructible.h
@@ -136,6 +136,19 @@ class Genode::Reconstructible : Noncopyable
 		 */
 		bool is_constructed() const { return constructed(); }
 
+		/**
+		 * Construct or destruct volatile object according to 'condition'
+		 */
+		template <typename... ARGS>
+		void conditional(bool condition, ARGS &&... args)
+		{
+			if (condition && !constructed())
+				construct(args...);
+
+			if (!condition && constructed())
+				destruct();
+		}
+
 		/**
 		 * Access contained object
 		 */
@@ -161,11 +174,8 @@ class Genode::Reconstructible : Noncopyable
 template <typename MT>
 struct Genode::Constructible : Reconstructible<MT>
 {
-	template <typename... ARGS>
-	Constructible(ARGS &&...)
-	:
-		Reconstructible<MT>((typename Reconstructible<MT>::Lazy *)nullptr)
-	{ }
+	Constructible()
+	: Reconstructible<MT>((typename Reconstructible<MT>::Lazy *)nullptr) { }
 };
 
 #endif /* _INCLUDE__UTIL__RECONSTRUCTIBLE_H_ */
diff --git a/repos/gems/src/app/depot_query/main.cc b/repos/gems/src/app/depot_query/main.cc
index f8372a665..21f43d8a8 100644
--- a/repos/gems/src/app/depot_query/main.cc
+++ b/repos/gems/src/app/depot_query/main.cc
@@ -166,10 +166,10 @@ struct Depot_query::Main
 
 	typedef Constructible<Expanding_reporter> Constructible_reporter;
 
-	Constructible_reporter _directory_reporter    { _env, "directory"    };
-	Constructible_reporter _blueprint_reporter    { _env, "blueprint"    };
-	Constructible_reporter _dependencies_reporter { _env, "dependencies" };
-	Constructible_reporter _user_reporter         { _env, "user"         };
+	Constructible_reporter _directory_reporter    { };
+	Constructible_reporter _blueprint_reporter    { };
+	Constructible_reporter _dependencies_reporter { };
+	Constructible_reporter _user_reporter         { };
 
 	template <typename T, typename... ARGS>
 	static void _construct_if(bool condition, Constructible<T> &obj, ARGS &&... args)