@@ -194,8 +194,8 @@ use core::hash::{Hash, Hasher};
194194use core:: marker:: { Tuple , Unsize } ;
195195use core:: mem:: { self , SizedTypeProperties } ;
196196use core:: ops:: {
197- AsyncFn , AsyncFnMut , AsyncFnOnce , CoerceUnsized , Coroutine , CoroutineState , Deref , DerefMut ,
198- DerefPure , DispatchFromDyn , LegacyReceiver ,
197+ AsyncFn , AsyncFnMut , AsyncFnOnce , CoerceUnsized , ControlFlow , Coroutine , CoroutineState , Deref ,
198+ DerefMut , DerefPure , DispatchFromDyn , FromResidual , LegacyReceiver , Residual , Try ,
199199} ;
200200use core:: pin:: { Pin , PinCoerceUnsized } ;
201201use core:: ptr:: { self , NonNull , Unique } ;
@@ -389,6 +389,95 @@ impl<T> Box<T> {
389389 pub fn try_new_zeroed ( ) -> Result < Box < mem:: MaybeUninit < T > > , AllocError > {
390390 Box :: try_new_zeroed_in ( Global )
391391 }
392+ 393+ /// Maps the value in a box, reusing the allocation if possible.
394+ ///
395+ /// `f` is called on the value in the box, and the result is returned, also boxed.
396+ ///
397+ /// Note: this is an associated function, which means that you have
398+ /// to call it as `Box::map(b, f)` instead of `b.map(f)`. This
399+ /// is so that there is no conflict with a method on the inner type.
400+ ///
401+ /// # Examples
402+ ///
403+ /// ```
404+ /// #![feature(smart_pointer_try_map)]
405+ ///
406+ /// let b = Box::new(7);
407+ /// let new = Box::map(b, |i| i + 7);
408+ /// assert_eq!(*new, 14);
409+ /// ```
410+ #[ unstable( feature = "smart_pointer_try_map" , issue = "144419" ) ]
411+ pub fn map < U > ( this : Self , f : impl FnOnce ( T ) -> U ) -> Box < U > {
412+ if size_of :: < T > ( ) == size_of :: < U > ( ) && align_of :: < T > ( ) == align_of :: < U > ( ) {
413+ let ptr = & raw const * this;
414+ unsafe {
415+ let new = f ( ptr. read ( ) ) ;
416+ let ptr = Box :: into_raw ( this) ;
417+ ptr. cast :: < U > ( ) . write ( new) ;
418+ Box :: from_raw ( ptr. cast :: < U > ( ) )
419+ }
420+ } else {
421+ Box :: new ( f ( * this) )
422+ }
423+ }
424+ 425+ /// Attempts to map the value in a box, reusing the allocation if possible.
426+ ///
427+ /// `f` is called on the value in the box, and if the operation succeeds, the result is
428+ /// returned, also boxed.
429+ ///
430+ /// Note: this is an associated function, which means that you have
431+ /// to call it as `Box::try_map(b, f)` instead of `b.try_map(f)`. This
432+ /// is so that there is no conflict with a method on the inner type.
433+ ///
434+ /// # Examples
435+ ///
436+ /// ```
437+ /// #![feature(smart_pointer_try_map)]
438+ ///
439+ /// let b = Box::new(7);
440+ /// let new = Box::try_map(b, u32::try_from).unwrap();
441+ /// assert_eq!(*new, 7);
442+ /// ```
443+ #[ unstable( feature = "smart_pointer_try_map" , issue = "144419" ) ]
444+ pub fn try_map < R > (
445+ this : Self ,
446+ f : impl FnOnce ( T ) -> R ,
447+ ) -> <R :: Residual as Residual < Box < R :: Output > > >:: TryType
448+ where
449+ R : Try ,
450+ R :: Residual : Residual < Box < R :: Output > > ,
451+ {
452+ if size_of :: < T > ( ) == size_of :: < R :: Output > ( ) && align_of :: < T > ( ) == align_of :: < R :: Output > ( ) {
453+ let ptr = & raw const * this;
454+ unsafe {
455+ let new = f ( ptr. read ( ) ) ;
456+ let ptr = Box :: into_raw ( this) ;
457+ match new. branch ( ) {
458+ ControlFlow :: Continue ( c) => {
459+ ptr. cast :: < R :: Output > ( ) . write ( c) ;
460+ <R :: Residual as Residual < Box < R :: Output > > >:: TryType :: from_output (
461+ Box :: from_raw ( ptr. cast :: < R :: Output > ( ) ) ,
462+ )
463+ }
464+ ControlFlow :: Break ( b) => {
465+ drop ( Box :: from_raw ( ptr) ) ;
466+ <R :: Residual as Residual < Box < R :: Output > > >:: TryType :: from_residual ( b)
467+ }
468+ }
469+ }
470+ } else {
471+ match f ( * this) . branch ( ) {
472+ ControlFlow :: Continue ( c) => {
473+ <R :: Residual as Residual < Box < R :: Output > > >:: TryType :: from_output ( Box :: new ( c) )
474+ }
475+ ControlFlow :: Break ( b) => {
476+ <R :: Residual as Residual < Box < R :: Output > > >:: TryType :: from_residual ( b)
477+ }
478+ }
479+ }
480+ }
392481}
393482
394483impl < T , A : Allocator > Box < T , A > {
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