Is there a way to get really smart code completion?
Well, the answer to your question is "Yes." You can implement the plugin or add this feature to an existing one. But right now, the only plugin used by default in QtCreator and dealing with code completion is ClangCodeModel.
The ClangCodeModel plugin does not have such a function.
On the other hand, having the installed plugin is not enough for it to work, you need to enable it.
Go to Help → About Plugins and make sure the “Download” checkbox for the ClangCodeModel plugin is checked.
The plugin improves code completion, but remember that this plugin is experimental and not complete.

Links of interest:
Code completion is not so smart.
Clan-Based Code Model
Raydel miranda
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