Struct proc_macro_kwargs::parse::ExplicitOption
source · pub struct ExplicitOption<T>(pub Option<T>);
Expand description
A version of Option
that is parsed with explicit Some(<inner>)
or None
syntax
This is as opposed to a regular Option
, which requires
no extra syntax and always parses to Some
(it’s intended for use with optional args)
Tuple Fields§
§0: Option<T>
Methods from Deref<Target = Option<T>>§
1.0.0 · sourcepub fn as_ref(&self) -> Option<&T>
pub fn as_ref(&self) -> Option<&T>
Converts from &Option<T>
to Option<&T>
.
§Examples
Calculates the length of an Option<String>
as an Option<usize>
without moving the String
. The map
method takes the self
argument by value,
consuming the original, so this technique uses as_ref
to first take an Option
to a
reference to the value inside the original.
let text: Option<String> = Some("Hello, world!".to_string());
// First, cast `Option<String>` to `Option<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `text` on the stack.
let text_length: Option<usize> = text.as_ref().map(|s| s.len());
println!("still can print text: {text:?}");
1.75.0 · sourcepub fn as_slice(&self) -> &[T]
pub fn as_slice(&self) -> &[T]
Returns a slice of the contained value, if any. If this is None
, an
empty slice is returned. This can be useful to have a single type of
iterator over an Option
or slice.
Note: Should you have an Option<&T>
and wish to get a slice of T
,
you can unpack it via opt.map_or(&[], std::slice::from_ref)
.
§Examples
assert_eq!(
[Some(1234).as_slice(), None.as_slice()],
[&[1234][..], &[][..]],
);
The inverse of this function is (discounting
borrowing) [_]::first
:
for i in [Some(1234_u16), None] {
assert_eq!(i.as_ref(), i.as_slice().first());
}
1.40.0 · sourcepub fn as_deref(&self) -> Option<&<T as Deref>::Target>where
T: Deref,
pub fn as_deref(&self) -> Option<&<T as Deref>::Target>where
T: Deref,
Converts from Option<T>
(or &Option<T>
) to Option<&T::Target>
.
Leaves the original Option in-place, creating a new one with a reference
to the original one, additionally coercing the contents via Deref
.
§Examples
let x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref(), Some("hey"));
let x: Option<String> = None;
assert_eq!(x.as_deref(), None);
Trait Implementations§
source§impl<T: Clone> Clone for ExplicitOption<T>
impl<T: Clone> Clone for ExplicitOption<T>
source§fn clone(&self) -> ExplicitOption<T>
fn clone(&self) -> ExplicitOption<T>
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl<T: Debug> Debug for ExplicitOption<T>
impl<T: Debug> Debug for ExplicitOption<T>
source§impl<T> Deref for ExplicitOption<T>
impl<T> Deref for ExplicitOption<T>
source§impl<T> From<ExplicitOption<T>> for Option<T>
impl<T> From<ExplicitOption<T>> for Option<T>
source§fn from(explicit: ExplicitOption<T>) -> Option<T>
fn from(explicit: ExplicitOption<T>) -> Option<T>
source§impl<T> From<Option<T>> for ExplicitOption<T>
impl<T> From<Option<T>> for ExplicitOption<T>
source§impl<T: Hash> Hash for ExplicitOption<T>
impl<T: Hash> Hash for ExplicitOption<T>
source§impl<T: MacroArg> MacroArg for ExplicitOption<T>
impl<T: MacroArg> MacroArg for ExplicitOption<T>
source§fn parse_macro_arg(stream: ParseStream<'_>) -> Result<Self>
fn parse_macro_arg(stream: ParseStream<'_>) -> Result<Self>
source§impl<T: PartialEq> PartialEq for ExplicitOption<T>
impl<T: PartialEq> PartialEq for ExplicitOption<T>
source§fn eq(&self, other: &ExplicitOption<T>) -> bool
fn eq(&self, other: &ExplicitOption<T>) -> bool
self
and other
values to be equal, and is used
by ==
.impl<T: Copy> Copy for ExplicitOption<T>
impl<T: Eq> Eq for ExplicitOption<T>
impl<T> StructuralPartialEq for ExplicitOption<T>
Auto Trait Implementations§
impl<T> Freeze for ExplicitOption<T>where
T: Freeze,
impl<T> RefUnwindSafe for ExplicitOption<T>where
T: RefUnwindSafe,
impl<T> Send for ExplicitOption<T>where
T: Send,
impl<T> Sync for ExplicitOption<T>where
T: Sync,
impl<T> Unpin for ExplicitOption<T>where
T: Unpin,
impl<T> UnwindSafe for ExplicitOption<T>where
T: UnwindSafe,
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> 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.