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use std::{mem, ptr}; /// Copied from `syntax::ptr::P` pub trait Map<T> { /// Transform the inner value, consuming `self` and producing a new `P<T>`. fn map<F>(self, f: F) -> Self where F: FnOnce(T) -> T; } impl<T> Map<T> for Box<T> { fn map<F>(mut self, f: F) -> Self where F: FnOnce(T) -> T, { let p: *mut T = &mut *self; // Leak self in case of panic. // FIXME(eddyb) Use some sort of "free guard" that // only deallocates, without dropping the pointee, // in case the call the `f` below ends in a panic. mem::forget(self); unsafe { ptr::write(p, f(ptr::read(p))); // Recreate self from the raw pointer. Box::from_raw(p) } } }