1 #![cfg(feature = "alloc")] 2 #![allow(missing_docs)] 3 4 use alloc::string::String; 5 use core::mem::{self, MaybeUninit}; 6 use core::ptr; 7 8 // ABI compatible with C++ rust::String (not necessarily alloc::string::String). 9 #[repr(C)] 10 pub struct RustString { 11 repr: [MaybeUninit<usize>; mem::size_of::<String>() / mem::size_of::<usize>()], 12 } 13 14 impl RustString { from(s: String) -> Self15 pub fn from(s: String) -> Self { 16 unsafe { mem::transmute::<String, RustString>(s) } 17 } 18 from_ref(s: &String) -> &Self19 pub fn from_ref(s: &String) -> &Self { 20 unsafe { &*(s as *const String as *const RustString) } 21 } 22 from_mut(s: &mut String) -> &mut Self23 pub fn from_mut(s: &mut String) -> &mut Self { 24 unsafe { &mut *(s as *mut String as *mut RustString) } 25 } 26 into_string(self) -> String27 pub fn into_string(self) -> String { 28 unsafe { mem::transmute::<RustString, String>(self) } 29 } 30 as_string(&self) -> &String31 pub fn as_string(&self) -> &String { 32 unsafe { &*(self as *const RustString as *const String) } 33 } 34 as_mut_string(&mut self) -> &mut String35 pub fn as_mut_string(&mut self) -> &mut String { 36 unsafe { &mut *(self as *mut RustString as *mut String) } 37 } 38 } 39 40 impl Drop for RustString { drop(&mut self)41 fn drop(&mut self) { 42 unsafe { ptr::drop_in_place(self.as_mut_string()) } 43 } 44 } 45 46 const_assert_eq!(mem::size_of::<[usize; 3]>(), mem::size_of::<RustString>()); 47 const_assert_eq!(mem::size_of::<String>(), mem::size_of::<RustString>()); 48 const_assert_eq!(mem::align_of::<String>(), mem::align_of::<RustString>()); 49