#[non_exhaustive]pub enum ScanDirection {
Backward,
Forward,
Unknown(UnknownVariantValue),
}
Expand description
When writing a match expression against ScanDirection
, it is important to ensure
your code is forward-compatible. That is, if a match arm handles a case for a
feature that is supported by the service but has not been represented as an enum
variant in a current version of SDK, your code should continue to work when you
upgrade SDK to a future version in which the enum does include a variant for that
feature.
Here is an example of how you can make a match expression forward-compatible:
# let scandirection = unimplemented!();
match scandirection {
ScanDirection::Backward => { /* ... */ },
ScanDirection::Forward => { /* ... */ },
other @ _ if other.as_str() == "NewFeature" => { /* handles a case for `NewFeature` */ },
_ => { /* ... */ },
}
The above code demonstrates that when scandirection
represents
NewFeature
, the execution path will lead to the second last match arm,
even though the enum does not contain a variant ScanDirection::NewFeature
in the current version of SDK. The reason is that the variable other
,
created by the @
operator, is bound to
ScanDirection::Unknown(UnknownVariantValue("NewFeature".to_owned()))
and calling as_str
on it yields "NewFeature"
.
This match expression is forward-compatible when executed with a newer
version of SDK where the variant ScanDirection::NewFeature
is defined.
Specifically, when scandirection
represents NewFeature
,
the execution path will hit the second last match arm as before by virtue of
calling as_str
on ScanDirection::NewFeature
also yielding "NewFeature"
.
Explicitly matching on the Unknown
variant should
be avoided for two reasons:
- The inner data
UnknownVariantValue
is opaque, and no further information can be extracted. - It might inadvertently shadow other intended match arms.
Variants (Non-exhaustive)§
This enum is marked as non-exhaustive
Backward
Forward
Unknown(UnknownVariantValue)
Unknown
. See the docs on this enum for the correct way to handle unknown variants.Unknown
contains new variants that have been added since this code was generated.
Implementations§
source§impl ScanDirection
impl ScanDirection
source§impl ScanDirection
impl ScanDirection
sourcepub fn try_parse(value: &str) -> Result<Self, UnknownVariantError>
pub fn try_parse(value: &str) -> Result<Self, UnknownVariantError>
Parses the enum value while disallowing unknown variants.
Unknown variants will result in an error.
Trait Implementations§
source§impl AsRef<str> for ScanDirection
impl AsRef<str> for ScanDirection
source§impl Clone for ScanDirection
impl Clone for ScanDirection
source§fn clone(&self) -> ScanDirection
fn clone(&self) -> ScanDirection
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl Debug for ScanDirection
impl Debug for ScanDirection
source§impl Display for ScanDirection
impl Display for ScanDirection
source§impl From<&str> for ScanDirection
impl From<&str> for ScanDirection
source§impl FromStr for ScanDirection
impl FromStr for ScanDirection
source§impl Hash for ScanDirection
impl Hash for ScanDirection
source§impl Ord for ScanDirection
impl Ord for ScanDirection
source§fn cmp(&self, other: &ScanDirection) -> Ordering
fn cmp(&self, other: &ScanDirection) -> Ordering
1.21.0 · source§fn max(self, other: Self) -> Selfwhere
Self: Sized,
fn max(self, other: Self) -> Selfwhere
Self: Sized,
source§impl PartialEq for ScanDirection
impl PartialEq for ScanDirection
source§fn eq(&self, other: &ScanDirection) -> bool
fn eq(&self, other: &ScanDirection) -> bool
self
and other
values to be equal, and is used
by ==
.source§impl PartialOrd for ScanDirection
impl PartialOrd for ScanDirection
source§fn partial_cmp(&self, other: &ScanDirection) -> Option<Ordering>
fn partial_cmp(&self, other: &ScanDirection) -> Option<Ordering>
1.0.0 · source§fn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
self
and other
) and is used by the <=
operator. Read moreimpl Eq for ScanDirection
impl StructuralPartialEq for ScanDirection
Auto Trait Implementations§
impl Freeze for ScanDirection
impl RefUnwindSafe for ScanDirection
impl Send for ScanDirection
impl Sync for ScanDirection
impl Unpin for ScanDirection
impl UnwindSafe for ScanDirection
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<Q, K> Comparable<K> for Q
impl<Q, K> Comparable<K> for Q
source§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
source§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
source§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
key
and return true
if they are equal.source§impl<T> Instrument for T
impl<T> Instrument for T
source§fn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
source§fn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
source§impl<T> IntoEither for T
impl<T> IntoEither for T
source§fn into_either(self, into_left: bool) -> Either<Self, Self>
fn into_either(self, into_left: bool) -> Either<Self, Self>
self
into a Left
variant of Either<Self, Self>
if into_left
is true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read moresource§fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
self
into a Left
variant of Either<Self, Self>
if into_left(&self)
returns true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read more