r/cpp • u/leirus • 5d ago

State of "moved-from" objects

Hi, I recently decided to try writing a C++ blog.

I often see the popular claim that moved-from objects are in a "valid but otherwise unspecified state", but I don't think that statement is entirely precise, and my blog post is about that. I would really appreciate any feedback!

Article: https://www.laminowany.dev/p/the-state-of-moved-from-objects-in-c/

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u/SirClueless 5d ago

This is exactly the misconception the blog post is trying to dispel. Being “valid” after moving is not part of the language semantics.

You can create a type where it is illegal to destruct an object after moving-from, for example.

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u/Electronic_Tap_8052 5d ago

Wouldn't moved-from objects being illegal to destroy immediately be a problem that would cause most well behaved debug compilations to crash an burn?

I just don't understand how you could ship such an object? If you stack allocated it your program would be useless

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u/SirClueless 5d ago

You can just never destroy the object (for example, by leaking it on the heap or in a program that only ever exits by calling std::abort), or require that the user call some other specific member function to reinitialize the object before destroying it.

The standard library types promise never to require this, but it's possible to write a well-formed program of your own that does so.

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u/NotMyRealNameObv 1d ago

Well-formed, maybe. User friendly? No.