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Struct HandleOrNull 

pub struct HandleOrNull(/* private fields */);
Available on Windows only.

FFI type for handles in return values or out parameters, where NULL is used as a sentry value to indicate errors, such as in the return value of CreateThread. This uses repr(transparent) and has the representation of a host handle, so that it can be used in such FFI declarations.

The only thing you can usefully do with a HandleOrNull is to convert it into an OwnedHandle using its TryFrom implementation; this conversion takes care of the check for NULL. This ensures that such FFI calls cannot start using the handle without checking for NULL first.

This type may hold any handle value that OwnedHandle may hold. As with OwnedHandle, when it holds -1, that value is interpreted as a valid handle value, such as the current process handle, and not INVALID_HANDLE_VALUE.

If this holds a non-null handle, it will close the handle on drop.

Implementations

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impl HandleOrNull
1.63.0Source
pub unsafe fn from_raw_handle(handle: RawHandle) -> Self

Constructs a new instance of Self from the given RawHandle returned from a Windows API that uses null to indicate failure, such as CreateThread.

Use HandleOrInvalid instead of HandleOrNull for APIs that use INVALID_HANDLE_VALUE to indicate failure.

Safety

The passed handle value must either satisfy the safety requirements of FromRawHandle::from_raw_handle, or be null. Note that not all Windows APIs use null for errors; see here for the full story.

Trait Implementations

1.63.0Source
impl Debug for HandleOrNull
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fn fmt(&self, f: &mut Formatter<'_>) -> Result
Formats the value using the given formatter. Read more
1.63.0Source
impl Drop for HandleOrNull
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fn drop(&mut self)
Executes the destructor for this type. Read more
1.63.0Source
impl TryFrom<HandleOrNull> for OwnedHandle
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type Error = NullHandleError
The type returned in the event of a conversion error.
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fn try_from(handle_or_null: HandleOrNull) -> Result<Self, NullHandleError>
Performs the conversion.
1.63.0Source
impl Send for HandleOrNull
1.63.0Source
impl Sync for HandleOrNull

Auto Trait Implementations

impl Freeze for HandleOrNull
impl RefUnwindSafe for HandleOrNull
impl Unpin for HandleOrNull
impl UnwindSafe for HandleOrNull

Blanket Implementations

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impl<T> Any for Twhere
    T: 'static + ?Sized,
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fn type_id(&self) -> TypeId
Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere
    T: ?Sized,
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fn borrow(&self) -> &T
Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere
    T: ?Sized,
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fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
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impl<T> From<T> for T
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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere
    U: From<T>,
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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for Twhere
    U: Into<T>,
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type Error = Infallible
The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
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impl<T, U> TryInto<U> for Twhere
    U: TryFrom<T>,
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type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/os/windows/io/struct.HandleOrNull.html