Why Pin is needed for self-referential Futures
WHAT IT TESTS: deep grasp of async internals. OUTLINE: async blocks compile to state machines that can hold references into their own storage; Pin guarantees the value will not move so those internal pointers stay valid across polls.
WHAT IT TESTS: whether you understand how the compiler lowers async blocks and why memory address stability matters. ANSWER OUTLINE: An async block becomes a generated state machine struct; if a borrow spans an await point, the struct holds a pointer into one of its own fields, making it self-referential. Moving such a struct would relocate the data while the internal pointer still points at the old address, creating a dangling pointer. Pin<&mut T> is a guarantee that the value will not move, so poll can rely on stable addresses.
Read the original → interview
- #rust
- #async
- #pin
- #futures
- #memory-safety
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