Install yasnippet and vala-snippets packages

elpa/yasnippet-20160924.2001/snippets/c++-mode/operator+=

@@ -0,0 +1,10 @@
+# -*- mode: snippet -*-
+# name: operator+=
+# key: +=
+# group: operator overloading
+# --
+${1:MyClass}& $1::operator+=(${2:const $1 &rhs})
+{
+  $0
+  return *this;
+}