example:calculator: Add property overrides

Add examples of how to override the get and set property calls.

Change-Id: I1436ed7c286aa141ffb63a6af8c4766bf764f74b
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/example/calculator-aserver.cpp b/example/calculator-aserver.cpp
index 9880e49..b0500de 100644
--- a/example/calculator-aserver.cpp
+++ b/example/calculator-aserver.cpp
@@ -1,6 +1,8 @@
 #include <net/poettering/Calculator/aserver.hpp>
 #include <sdbusplus/async.hpp>
 
+#include <iostream>
+
 class Calculator :
     public sdbusplus::aserver::net::poettering::Calculator<Calculator>
 {
@@ -38,6 +40,19 @@
         cleared(v);
         co_return;
     }
+
+    auto get_property(owner_t) const
+    {
+        std::cout << " get_property on owner\n";
+        return owner_;
+    }
+
+    bool set_property(owner_t, auto owner)
+    {
+        std::cout << " set_property on owner\n";
+        std::swap(owner_, owner);
+        return owner_ == owner;
+    }
 };
 
 int main()
diff --git a/example/calculator-client.cpp b/example/calculator-client.cpp
index 0ba1438..0c9b3ad 100644
--- a/example/calculator-client.cpp
+++ b/example/calculator-client.cpp
@@ -50,6 +50,15 @@
         std::cout << "Should be 1234: " << _ << std::endl;
     }
 
+    {
+        co_await c.owner("client");
+    }
+
+    {
+        auto _ = co_await c.owner();
+        std::cout << "Should be 'client': " << _ << std::endl;
+    }
+
     co_return;
 }