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But that's the problem, you didn't say explicitly what it should be. If the right side gets accidentally changed, nothing is going to complain if what it got changed to supports the same interface (not terribly uncommon in the modern world if lots and lots of operator driven stuff.)
If you explicitly say what it's supposed to be, then two things have to get simultaneous broken in the same way. If you don't, then only one has to get broken for potential silent errors.
If that was the case I wouldn't use auto . The situation you described is actually a feature of the auto keyword. It's pretty useful to only change the initializer without have to change the type declaration during refactoring.
I don't think the point of a language should to make it easy to refactor without having to really think about what you are doing and the potential silent errors it could introduce. Significant refactoring isn't common and it should be approached very carefully. Being explicit it always safer.
I remember trying to install Mathematica, which uses some library that is distributed with VC++, and there had been so many installs over the years that it just wouldn't work. I had to do a whole OS system wipe to get it to work.
I think they just hop to it, buck up and get the job done.
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