Consider this code: #include <iostream> void p(const std::string &x) { std::cout << x << std::endl; } int main() { p(

Consider this code: #include <iostream> void p(const std::string &x) { std::cout << x << std::endl; } int main() { p("hello"); } Neither p, which takes an already-allocated std::string, nor main, which uses a string literal, explicitly/obviously requests dynamic memory allocation. Yet it happens. In userspace, that's not a huge problem - even if allocation requires asking for more memory from the kernel, which requires paging out some dirty files to disk, which blocks for a few seconds on NFS, that's fine - the kernel will just suspend the userspace process for a few seconds while all that happens. Inside the pager or NFS implementation, though, an unintentional memory allocation can deadlock the whole system. In Rust you'd have to write .to_owned() to do the equivalent, and it would be obvious that doing it in code that might be responsible for freeing up memory is a mistake.