Struct RangeFrom

pub struct RangeFrom<Idx> {
    pub start: Idx,
}

A range only bounded inclusively below (start..).

The RangeFrom start.. contains all values with x >= start.

Note: Overflow in the Iterator implementation (when the contained data type reaches its numerical limit) is allowed to panic, wrap, or saturate. This behavior is defined by the implementation of the Step trait. For primitive integers, this follows the normal rules, and respects the overflow checks profile (panic in debug, wrap in release). Note also that overflow happens earlier than you might assume: the overflow happens in the call to next that yields the maximum value, as the range must be set to a state to yield the next value.

Examples

The start.. syntax is a RangeFrom:

assert_eq!((2..), std::ops::RangeFrom { start: 2 });
assert_eq!(2 + 3 + 4, (2..).take(3).sum());

let arr = [0, 1, 2, 3, 4];
assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
assert_eq!(arr[ .. 3], [0, 1, 2      ]);
assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
assert_eq!(arr[1..  ], [   1, 2, 3, 4]); // This is a `RangeFrom`
assert_eq!(arr[1.. 3], [   1, 2      ]);
assert_eq!(arr[1..=3], [   1, 2, 3   ]);

Fields

start: Idx

The lower bound of the range (inclusive).

Implementations

impl<Idx: PartialOrd<Idx>> RangeFrom<Idx>

pub fn contains<U>(&self, item: &U) -> bool

where Idx: PartialOrd<U>, U: ?Sized + PartialOrd<Idx>,

Returns true if item is contained in the range.

Examples

assert!(!(3..).contains(&2));
assert!( (3..).contains(&3));
assert!( (3..).contains(&1_000_000_000));

assert!( (0.0..).contains(&0.5));
assert!(!(0.0..).contains(&f32::NAN));
assert!(!(f32::NAN..).contains(&0.5));

Trait Implementations

impl<Idx: Clone> Clone for RangeFrom<Idx>

fn clone(&self) -> RangeFrom<Idx>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

where Self:,

Performs copy-assignment from source.

impl<Idx: Debug> Debug for RangeFrom<Idx>

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> From<RangeFrom<T>> for RangeFrom<T>

fn from(value: RangeFrom<T>) -> Self

Converts to this type from the input type.

impl<T> From<RangeFrom<T>> for RangeFrom<T>

fn from(value: RangeFrom<T>) -> Self

Converts to this type from the input type.

impl<Idx: Hash> Hash for RangeFrom<Idx>

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H: Hasher>(data: &[Self], state: &mut H)

where Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Index<RangeFrom<usize>> for CStr

type Output = CStr

The returned type after indexing.

fn index(&self, index: RangeFrom<usize>) -> &CStr

Performs the indexing (container[index]) operation.

impl<T> IntoBounds<T> for RangeFrom<T>

fn into_bounds(self) -> (Bound<T>, Bound<T>)

🔬This is a nightly-only experimental API. (range_into_bounds #136903)

Convert this range into the start and end bounds. Returns (start_bound, end_bound).

fn intersect<R>(self, other: R) -> (Bound<T>, Bound<T>)

where Self: Sized, T: Ord, R: Sized + IntoBounds<T>,

🔬This is a nightly-only experimental API. (range_into_bounds #136903)

Compute the intersection of self and other.

impl<A: Step> Iterator for RangeFrom<A>

type Item = A

The type of the elements being iterated over.

fn next(&mut self) -> Option<A>

Advances the iterator and returns the next value.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the iterator.

fn nth(&mut self, n: usize) -> Option<A>

Returns the nth element of the iterator.

fn next_chunk<const N: usize>( &mut self, ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_next_chunk #98326)

Advances the iterator and returns an array containing the next N values.

fn count(self) -> usize

where Self: Sized,

Consumes the iterator, counting the number of iterations and returning it.

fn last(self) -> Option<Self::Item>

where Self: Sized,

Consumes the iterator, returning the last element.

fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>

🔬This is a nightly-only experimental API. (iter_advance_by #77404)

Advances the iterator by n elements.

fn step_by(self, step: usize) -> StepBy<Self>

where Self: Sized,

Creates an iterator starting at the same point, but stepping by the given amount at each iteration.

fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter>

where Self: Sized, U: IntoIterator<Item = Self::Item>,

Takes two iterators and creates a new iterator over both in sequence.

fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter>

where Self: Sized, U: IntoIterator,

‘Zips up’ two iterators into a single iterator of pairs.

fn intersperse(self, separator: Self::Item) -> Intersperse<Self>

where Self: Sized, Self::Item: Clone,

🔬This is a nightly-only experimental API. (iter_intersperse #79524)

Creates a new iterator which places a copy of separator between adjacent items of the original iterator.

fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>

where Self: Sized, G: FnMut() -> Self::Item,

🔬This is a nightly-only experimental API. (iter_intersperse #79524)

Creates a new iterator which places an item generated by separator between adjacent items of the original iterator.

fn map<B, F>(self, f: F) -> Map<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> B,

Takes a closure and creates an iterator which calls that closure on each element.

fn for_each<F>(self, f: F)

where Self: Sized, F: FnMut(Self::Item),

Calls a closure on each element of an iterator.

fn filter<P>(self, predicate: P) -> Filter<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator which uses a closure to determine if an element should be yielded.

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate<Self>

where Self: Sized,

Creates an iterator which gives the current iteration count as well as the next value.

fn peekable(self) -> Peekable<Self>

where Self: Sized,

Creates an iterator which can use the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information.

fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that skips elements based on a predicate.

fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate.

fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P>

where Self: Sized, P: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both yields elements based on a predicate and maps.

fn skip(self, n: usize) -> Skip<Self>

where Self: Sized,

Creates an iterator that skips the first n elements.

fn take(self, n: usize) -> Take<Self>

where Self: Sized,

Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner.

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>

where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,

An iterator adapter which, like fold, holds internal state, but unlike fold, produces a new iterator.

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>

where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,

Creates an iterator that works like map, but flattens nested structure.

fn flatten(self) -> Flatten<Self>

where Self: Sized, Self::Item: IntoIterator,

Creates an iterator that flattens nested structure.

fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N>

where Self: Sized, F: FnMut(&[Self::Item; N]) -> R,

🔬This is a nightly-only experimental API. (iter_map_windows #87155)

Calls the given function f for each contiguous window of size N over self and returns an iterator over the outputs of f. Like slice::windows(), the windows during mapping overlap as well.

fn fuse(self) -> Fuse<Self>

where Self: Sized,

Creates an iterator which ends after the first None.

fn inspect<F>(self, f: F) -> Inspect<Self, F>

where Self: Sized, F: FnMut(&Self::Item),

Does something with each element of an iterator, passing the value on.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Iterator.

fn collect<B: FromIterator<Self::Item>>(self) -> B

where Self: Sized,

Transforms an iterator into a collection.

fn try_collect<B>(&mut self) -> <Self::Item::Residual as Residual<B>>::TryType

where Self: Sized, Self::Item: Try<Residual: Residual<B>>, B: FromIterator<<Self::Item as Try>::Output>,

🔬This is a nightly-only experimental API. (iterator_try_collect #94047)

Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered.

fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut E

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_collect_into #94780)

Collects all the items from an iterator into a collection.

fn partition<B, F>(self, f: F) -> (B, B)

where Self: Sized, B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool,

Consumes an iterator, creating two collections from it.

fn is_partitioned<P>(self, predicate: P) -> bool

where Self: Sized, P: FnMut(Self::Item) -> bool,

🔬This is a nightly-only experimental API. (iter_is_partitioned #62544)

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false.

fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R

where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Output = B>,

An iterator method that applies a function as long as it returns successfully, producing a single, final value.

fn try_for_each<F, R>(&mut self, f: F) -> R

where Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Output = ()>,

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error.

fn fold<B, F>(self, init: B, f: F) -> B

where Self: Sized, F: FnMut(B, Self::Item) -> B,

Folds every element into an accumulator by applying an operation, returning the final result.

fn reduce<F>(self, f: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item,

Reduces the elements to a single one, by repeatedly applying a reducing operation.

fn try_reduce<R>( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <R::Residual as Residual<Option<R::Output>>>::TryType

where Self: Sized, R: Try<Output = Self::Item, Residual: Residual<Option<Self::Item>>>,

🔬This is a nightly-only experimental API. (iterator_try_reduce #87053)

Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately.

fn all<F>(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if every element of the iterator matches a predicate.

fn any<F>(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if any element of the iterator matches a predicate.

fn find<P>(&mut self, predicate: P) -> Option<Self::Item>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator that satisfies a predicate.

fn find_map<B, F>(&mut self, f: F) -> Option<B>

where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Applies function to the elements of iterator and returns the first non-none result.

fn try_find<R>( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <R::Residual as Residual<Option<Self::Item>>>::TryType

where Self: Sized, R: Try<Output = bool, Residual: Residual<Option<Self::Item>>>,

🔬This is a nightly-only experimental API. (try_find #63178)

Applies function to the elements of iterator and returns the first true result or the first error.

fn position<P>(&mut self, predicate: P) -> Option<usize>

where Self: Sized, P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator, returning its index.

fn max(self) -> Option<Self::Item>

where Self: Sized, Self::Item: Ord,

Returns the maximum element of an iterator.

fn min(self) -> Option<Self::Item>

where Self: Sized, Self::Item: Ord,

Returns the minimum element of an iterator.

fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the maximum value from the specified function.

fn max_by<F>(self, compare: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the maximum value with respect to the specified comparison function.

fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the minimum value from the specified function.

fn min_by<F>(self, compare: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the minimum value with respect to the specified comparison function.

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)

where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Iterator<Item = (A, B)>,

Converts an iterator of pairs into a pair of containers.

fn copied<'a, T>(self) -> Copied<Self>

where Self: Sized + Iterator<Item = &'a T>, T: Copy + 'a,

Creates an iterator which copies all of its elements.

fn cloned<'a, T>(self) -> Cloned<Self>

where Self: Sized + Iterator<Item = &'a T>, T: Clone + 'a,

Creates an iterator which clones all of its elements.

fn cycle(self) -> Cycle<Self>

where Self: Sized + Clone,

Repeats an iterator endlessly.

fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_array_chunks #100450)

Returns an iterator over N elements of the iterator at a time.

fn sum<S>(self) -> S

where Self: Sized, S: Sum<Self::Item>,

Sums the elements of an iterator.

fn product<P>(self) -> P

where Self: Sized, P: Product<Self::Item>,

Iterates over the entire iterator, multiplying all the elements

fn cmp<I>(self, other: I) -> Ordering

where I: IntoIterator<Item = Self::Item>, Self::Item: Ord, Self: Sized,

Lexicographically compares the elements of this Iterator with those of another.

fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, I::Item) -> Ordering,

🔬This is a nightly-only experimental API. (iter_order_by #64295)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

fn partial_cmp<I>(self, other: I) -> Option<Ordering>

where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized,

Lexicographically compares the PartialOrd elements of this Iterator with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned.

fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, I::Item) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (iter_order_by #64295)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

fn eq<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialEq<I::Item>, Self: Sized,

Determines if the elements of this Iterator are equal to those of another.

fn eq_by<I, F>(self, other: I, eq: F) -> bool

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, I::Item) -> bool,

🔬This is a nightly-only experimental API. (iter_order_by #64295)

Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function.

fn ne<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialEq<I::Item>, Self: Sized,

Determines if the elements of this Iterator are not equal to those of another.

fn lt<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically less than those of another.

fn le<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically less or equal to those of another.

fn gt<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically greater than those of another.

fn ge<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically greater than or equal to those of another.

fn is_sorted(self) -> bool

where Self: Sized, Self::Item: PartialOrd,

Checks if the elements of this iterator are sorted.

fn is_sorted_by<F>(self, compare: F) -> bool

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> bool,

Checks if the elements of this iterator are sorted using the given comparator function.

fn is_sorted_by_key<F, K>(self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> K, K: PartialOrd,

Checks if the elements of this iterator are sorted using the given key extraction function.

impl<T> OneSidedRange<T> for RangeFrom<T>

where Self: RangeBounds<T>,

fn bound(self) -> (OneSidedRangeBound, T)

🔬This is a nightly-only experimental API. (one_sided_range #69780)

An internal-only helper function for split_off and split_off_mut that returns the bound of the one-sided range.

impl<Idx: PartialEq> PartialEq for RangeFrom<Idx>

fn eq(&self, other: &RangeFrom<Idx>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> RangeBounds<T> for RangeFrom<&T>

fn start_bound(&self) -> Bound<&T>

Start index bound.

fn end_bound(&self) -> Bound<&T>

End index bound.

fn contains<U>(&self, item: &U) -> bool

where T: PartialOrd<U>, U: ?Sized + PartialOrd<T>,

Returns true if item is contained in the range.

fn is_empty(&self) -> bool

where T: PartialOrd,

🔬This is a nightly-only experimental API. (range_bounds_is_empty #137300)

Returns true if the range contains no items. One-sided ranges (RangeFrom, etc) always return false.

impl<T> RangeBounds<T> for RangeFrom<T>

fn start_bound(&self) -> Bound<&T>

Start index bound.

fn end_bound(&self) -> Bound<&T>

End index bound.

fn contains<U>(&self, item: &U) -> bool

where T: PartialOrd<U>, U: ?Sized + PartialOrd<T>,

Returns true if item is contained in the range.

fn is_empty(&self) -> bool

where T: PartialOrd,

🔬This is a nightly-only experimental API. (range_bounds_is_empty #137300)

Returns true if the range contains no items. One-sided ranges (RangeFrom, etc) always return false.

impl<T> SliceIndex<[T]> for RangeFrom<usize>

The methods index and index_mut panic if the start of the range is out of bounds.

type Output = [T]

The output type returned by methods.

fn get(self, slice: &[T]) -> Option<&[T]>

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a shared reference to the output at this location, if in bounds.

fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]>

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable reference to the output at this location, if in bounds.

unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T]

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a pointer to the output at this location, without performing any bounds checking.

unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T]

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable pointer to the output at this location, without performing any bounds checking.

fn index(self, slice: &[T]) -> &[T]

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a shared reference to the output at this location, panicking if out of bounds.

fn index_mut(self, slice: &mut [T]) -> &mut [T]

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable reference to the output at this location, panicking if out of bounds.

impl SliceIndex<ByteStr> for RangeFrom<usize>

type Output = ByteStr

The output type returned by methods.

fn get(self, slice: &ByteStr) -> Option<&Self::Output>

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a shared reference to the output at this location, if in bounds.

fn get_mut(self, slice: &mut ByteStr) -> Option<&mut Self::Output>

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable reference to the output at this location, if in bounds.

unsafe fn get_unchecked(self, slice: *const ByteStr) -> *const Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a pointer to the output at this location, without performing any bounds checking.

unsafe fn get_unchecked_mut(self, slice: *mut ByteStr) -> *mut Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable pointer to the output at this location, without performing any bounds checking.

fn index(self, slice: &ByteStr) -> &Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a shared reference to the output at this location, panicking if out of bounds.

fn index_mut(self, slice: &mut ByteStr) -> &mut Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable reference to the output at this location, panicking if out of bounds.

impl SliceIndex<str> for RangeFrom<usize>

Implements substring slicing with syntax &self[begin ..] or &mut self[begin ..].

Returns a slice of the given string from the byte range [begin, len). Equivalent to &self[begin .. len] or &mut self[begin .. len].

This operation is O(1).

Prior to 1.20.0, these indexing operations were still supported by direct implementation of Index and IndexMut.

Panics

Panics if begin does not point to the starting byte offset of a character (as defined by is_char_boundary), or if begin > len.

type Output = str

The output type returned by methods.

fn get(self, slice: &str) -> Option<&Self::Output>

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a shared reference to the output at this location, if in bounds.

fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output>

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable reference to the output at this location, if in bounds.

unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a pointer to the output at this location, without performing any bounds checking.

unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable pointer to the output at this location, without performing any bounds checking.

fn index(self, slice: &str) -> &Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a shared reference to the output at this location, panicking if out of bounds.

fn index_mut(self, slice: &mut str) -> &mut Self::Output

🔬This is a nightly-only experimental API. (slice_index_methods)

Returns a mutable reference to the output at this location, panicking if out of bounds.

impl<Idx: Eq> Eq for RangeFrom<Idx>

impl<A: Step> FusedIterator for RangeFrom<A>

impl<Idx> StructuralPartialEq for RangeFrom<Idx>

impl<A: TrustedStep> TrustedLen for RangeFrom<A>