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use core::fmt;
use core::mem::ManuallyDrop;
#[repr(C)]
union DiplomatResultValue<T, E> {
ok: ManuallyDrop<T>,
err: ManuallyDrop<E>,
}
/// A [`Result`]-like type that can be passed across the FFI boundary
/// as a value. Used internally to return [`Result`]s and [`Option`]s
/// from functions.
#[repr(C)]
pub struct DiplomatResult<T, E> {
value: DiplomatResultValue<T, E>,
pub is_ok: bool,
}
/// A type to represent Option<T> over FFI.
///
/// Used internally to handle `Option<T>` arguments and return types, and needs to be
/// used explicitly for optional struct fields.
pub type DiplomatOption<T> = DiplomatResult<T, ()>;
impl<T, E> DiplomatResult<T, E> {
pub fn as_ref(&self) -> Result<&T, &E> {
// Safety: we're only accessing the union variants when the flag is correct
unsafe {
if self.is_ok {
Ok(&self.value.ok)
} else {
Err(&self.value.err)
}
}
}
}
impl<T> DiplomatOption<T> {
/// Helper for converting into an Option to avoid trait ambiguity errors with Into
#[inline]
pub fn into_option(self) -> Option<T> {
self.into()
}
/// Helper for converting into an Option with the inner type converted
#[inline]
pub fn into_converted_option<U: From<T>>(self) -> Option<U> {
self.into_option().map(Into::into)
}
}
impl<T: Clone, E: Clone> Clone for DiplomatResult<T, E> {
fn clone(&self) -> Self {
unsafe {
if self.is_ok {
Ok((*self.value.ok).clone()).into()
} else {
Err((*self.value.err).clone()).into()
}
}
}
}
impl<T, E> Drop for DiplomatResult<T, E> {
fn drop(&mut self) {
unsafe {
if self.is_ok {
let _ = ManuallyDrop::take(&mut self.value.ok);
} else {
let _ = ManuallyDrop::take(&mut self.value.err);
}
}
}
}
impl<T, E> From<Result<T, E>> for DiplomatResult<T, E> {
fn from(result: Result<T, E>) -> Self {
match result {
Result::Ok(ok) => DiplomatResult {
value: DiplomatResultValue {
ok: ManuallyDrop::new(ok),
},
is_ok: true,
},
Result::Err(err) => DiplomatResult {
value: DiplomatResultValue {
err: ManuallyDrop::new(err),
},
is_ok: false,
},
}
}
}
impl<T> From<Option<T>> for DiplomatOption<T> {
fn from(option: Option<T>) -> Self {
option.ok_or(()).into()
}
}
impl<T> From<DiplomatOption<T>> for Option<T> {
fn from(result: DiplomatOption<T>) -> Self {
Result::<T, ()>::from(result).ok()
}
}
impl<T, E> From<DiplomatResult<T, E>> for Result<T, E> {
fn from(mut result: DiplomatResult<T, E>) -> Result<T, E> {
unsafe {
if result.is_ok {
Ok(ManuallyDrop::take(&mut result.value.ok))
} else {
Err(ManuallyDrop::take(&mut result.value.err))
}
}
}
}
impl<T: fmt::Debug, E: fmt::Debug> fmt::Debug for DiplomatResult<T, E> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.as_ref().fmt(f)
}
}