From 2c8f93fb44cd08a6210f2b06d62ffb98677e7968 Mon Sep 17 00:00:00 2001
From: Vernon Mauery <vernon.mauery@linux.intel.com>
Date: Wed, 5 Sep 2018 12:02:39 -0700
Subject: sdbusplus::asio: fix callback with void args specialization

Callbacks with no arguments failed to build due to an error in the
utility::get_first_arg template. It failed to provide a type member for
the void specialization. With this fix, it is possible to have a handler
that has no arguments.

Tested by: Added a new callback to the asio-example.cpp. Without the
           template change, this caused the build to fail as expected.
           After adding the template change, the build succeeds and the
           example runs as expected.

Change-Id: Ib09b58c76df8cba57dc093ab37a4c1b68ea11ad3
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
---
 example/asio-example.cpp          | 7 +++++++
 sdbusplus/utility/type_traits.hpp | 1 +
 2 files changed, 8 insertions(+)

diff --git a/example/asio-example.cpp b/example/asio-example.cpp
index 31b55f2..354c7b0 100644
--- a/example/asio-example.cpp
+++ b/example/asio-example.cpp
@@ -17,6 +17,11 @@ int methodWithMessage(sdbusplus::message::message& m, int test)
     return ++test;
 }
 
+int voidBar(void)
+{
+    return 42;
+}
+
 int main()
 {
     using GetSubTreeType = std::vector<std::pair<
@@ -121,6 +126,8 @@ int main()
 
     iface->register_method("TestMethodWithMessage", methodWithMessage);
 
+    iface->register_method("VoidFunctionReturnsInt", voidBar);
+
     iface->initialize();
     iface->set_property("int", 45);
     io.run();
diff --git a/sdbusplus/utility/type_traits.hpp b/sdbusplus/utility/type_traits.hpp
index fb6f0b6..2d60972 100644
--- a/sdbusplus/utility/type_traits.hpp
+++ b/sdbusplus/utility/type_traits.hpp
@@ -38,6 +38,7 @@ struct strip_first_arg<std::tuple<FirstArg, Rest...>>
 template <typename T>
 struct get_first_arg
 {
+    using type = void;
 };
 
 template <typename FirstArg, typename... Rest>
-- 
cgit v1.2.3