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If you don't understand what placement new is, you don't know whether libraries using placement new affects you.

I did not write this comment about placement new specifically. It's just a thing that annoys me about the "learn a subset" idea. You still need to know at least enough about every feature to know whether it affects you. Placement new is perhaps not the best example there because it is relatively niche and self contained, true.

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If you don't understand all the 10s of million of line of linux code, you don't know whether you are using linux correctly.

If you're going to try to be clever/snide, at least come up with a better analogy...

Using Linux effectively doesn't mean you need to learn its source code. You need to know about its features (and trade-off, etc).

You don't need to know a language implementation's (e.g. gcc/clang for C++) source code to use a language well either, do you? Obviously you don't; it's a fools errand if all you ever want is to use it effectively.

You need to know about features (and trade-off, etc), how they were designed in isolation, and more importantly how they were designed to fit/connect together.

Show me some basic code using std vector that would change if the programmer knew more about placement new.

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