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> compiler will reject programs that use the moved-from value. Yes, this is something the C++ 'language' is not going to specify other than claiming that it is

• ninkendo 1y ago
  But it's not undefined behavior. That's the key. It's "unspecified behavior", meaning that according to the standard, it's allowed. A program that reuses a moved-from value is considered valid and well-formed by the standard. It merely delegates how to make this work to the individual implementation (a string becomes an empty string, a vector becomes an empty vector, etc.) The RFC you posted has nothing to do with move semantics, it's about references outliving what they point to (ie. use-after-free, etc) and similar to Rust's borrow checker. But here's the thing: move semantics and the borrow checker have nothing to do with each other! The borrow checker ensures that borrowed data (ie. &Foo, equivalent to C++'s references) is sound, it's not the part that enforces move semantics. That happens earlier in the compilation, the compiler enforces moves well before the borrow checker phase.