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C++ could adopt the UFCS universal-function-call feature of D-language that allows any ordinary free function to be called as if they were methods, without any special kind of type annotation.
It really couldn't. It would be a breaking change.
The way it was worded in the GP comment would change name lookup in existing well-formed programs, making them fail to compile, or compile differently.
I'm not familiar with Stroustrup's proposal, but I doubt that he proposed it without some opt-in annotation.
It really couldn't. It would be a breaking change.