Install yasnippet and vala-snippets packages

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

@@ -0,0 +1,9 @@
+# -*- mode: snippet -*-
+# name: operator!=
+# key: !=
+# group: operator overloading
+# --
+bool ${1:MyClass}::operator!=(const $1 &other) const
+{
+    return !(*this == other);
+}