protocol LazySequenceType
Inheritance |
SequenceType
View Protocol Hierarchy →
|
---|---|
Associated Types |
Elements : SequenceType = Self
A See Also: |
Import | import Swift |
Instance Variables
Deprecated: Will be removed in Swift 3.
Declaration
var array: [Self.Generator.Element] { get }
A sequence containing the same elements as this one, possibly with a simpler type.
When implementing lazy operations, wrapping elements
instead
of self
can prevent result types from growing an extra
LazySequence
layer. For example,
prext example needed
Note: this property need not be implemented by conforming types,
it has a default implementation in a protocol extension that
just returns self
.
Declaration
var elements: Self.Elements { get }
Instance Methods
Returns a subsequence containing all but the first n
elements.
Requires: n >= 0
Complexity: O(n
)
Declaration
func dropFirst(n: Int) -> Self.SubSequence
Declared In
SequenceType
Returns a subsequence containing all but the last n
elements.
Requires: self
is a finite sequence.
Requires: n >= 0
Complexity: O(self.count
)
Declaration
func dropLast(n: Int) -> Self.SubSequence
Declared In
SequenceType
Returns an Array
containing the elements of self
,
in order, that satisfy the predicate includeElement
.
Declaration
func filter(@noescape includeElement: (Self.Generator.Element) throws -> Bool) rethrows -> [Self.Generator.Element]
Declared In
SequenceType
Call body
on each element in self
in the same order as a
for-in loop.
sequence.forEach {
// body code
}
is similar to:
for element in sequence {
// body code
}
Note: You cannot use the break
or continue
statement to exit the
current call of the body
closure or skip subsequent calls.
Note: Using the return
statement in the body
closure will only
exit from the current call to body
, not any outer scope, and won't
skip subsequent calls.
Complexity: O(self.count
)
Declaration
func forEach(@noescape body: (Self.Generator.Element) throws -> Void) rethrows
Declared In
SequenceType
Returns a generator over the elements of this sequence.
Complexity: O(1).
Declaration
func generate() -> Self.Generator
Declared In
SequenceType
Returns an Array
containing the results of mapping transform
over self
.
Complexity: O(N).
Declaration
func map<T>(@noescape transform: (Self.Generator.Element) throws -> T) rethrows -> [T]
Declared In
SequenceType
Returns a subsequence, up to maxLength
in length, containing the
initial elements.
If maxLength
exceeds self.count
, the result contains all
the elements of self
.
Requires: maxLength >= 0
Declaration
func prefix(maxLength: Int) -> Self.SubSequence
Declared In
SequenceType
Returns the maximal SubSequence
s of self
, in order, that
don't contain elements satisfying the predicate isSeparator
.
maxSplit
: The maximum number of SubSequence
s to
return, minus 1.
If maxSplit + 1
SubSequence
s are returned, the last one is
a suffix of self
containing the remaining elements.
The default value is Int.max
.
allowEmptySubsequences
: If true
, an empty SubSequence
is produced in the result for each pair of consecutive elements
satisfying isSeparator
.
The default value is false
.
Requires: maxSplit >= 0
Declaration
func split(maxSplit: Int, allowEmptySlices: Bool, @noescape isSeparator: (Self.Generator.Element) throws -> Bool) rethrows -> [Self.SubSequence]
Declared In
SequenceType
Returns a slice, up to maxLength
in length, containing the
final elements of s
.
If maxLength
exceeds s.count
, the result contains all
the elements of s
.
Requires: self
is a finite sequence.
Requires: maxLength >= 0
Declaration
func suffix(maxLength: Int) -> Self.SubSequence
Declared In
SequenceType
Returns a value less than or equal to the number of elements in
self
, nondestructively.
Complexity: O(N).
Declaration
func underestimateCount() -> Int
Declared In
SequenceType
Default Implementations
Returns true
iff an element in self
satisfies predicate
.
Declaration
func contains(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Bool
Declared In
SequenceType
Returns a subsequence containing all but the first element.
Complexity: O(1)
Declaration
func dropFirst() -> Self.SubSequence
Declared In
SequenceType
Returns a subsequence containing all but the last element.
Requires: self
is a finite sequence.
Complexity: O(self.count
)
Declaration
func dropLast() -> Self.SubSequence
Declared In
SequenceType
Returns true
iff self
and other
contain equivalent elements, using
isEquivalent
as the equivalence test.
Requires: isEquivalent
is an
equivalence relation.
Declaration
func elementsEqual<OtherSequence : SequenceType where OtherSequence.Generator.Element == Generator.Element>(other: OtherSequence, @noescape isEquivalent: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Bool
Declared In
SequenceType
Returns a lazy SequenceType
containing pairs (n, x), where
ns are consecutive Int
s starting at zero, and xs are
the elements of base
:
> for (n, c) in "Swift".characters.enumerate() {
print("\(n): '\(c)'")
}
0: 'S'
1: 'w'
2: 'i'
3: 'f'
4: 't'
Declaration
func enumerate() -> EnumerateSequence<Self>
Declared In
SequenceType
Returns the elements of self
that satisfy predicate
.
Note: The elements of the result are computed on-demand, as
the result is used. No buffering storage is allocated and each
traversal step invokes predicate
on one or more underlying
elements.
Declaration
func filter(predicate: (Self.Elements.Generator.Element) -> Bool) -> LazyFilterSequence<Self.Elements>
Declared In
LazySequenceType
, SequenceType
Returns an Array
containing the non-nil results of mapping
transform
over self
.
Complexity: O(M + N), where M is the length of self
and N is the length of the result.
Declaration
func flatMap<T>(@noescape transform: (Self.Generator.Element) throws -> T?) rethrows -> [T]
Declared In
SequenceType
Returns an Array
containing the concatenated results of mapping
transform
over self
.
s.flatMap(transform)
is equivalent to
Array(s.map(transform).flatten())
Complexity: O(M + N), where M is the length of self
and N is the length of the result.
Declaration
func flatMap<S : SequenceType>(transform: (Self.Generator.Element) throws -> S) rethrows -> [S.Generator.Element]
Declared In
SequenceType
Returns the concatenated results of mapping transform
over
self
. Equivalent to
self.map(transform).flatten()
Complexity: O(1)
Declaration
func flatMap<Intermediate : SequenceType>(transform: (Self.Elements.Generator.Element) -> Intermediate) -> LazySequence<FlattenSequence<LazyMapSequence<Self.Elements, Intermediate>>>
Call body
on each element in self
in the same order as a
for-in loop.
sequence.forEach {
// body code
}
is similar to:
for element in sequence {
// body code
}
Note: You cannot use the break
or continue
statement to exit the
current call of the body
closure or skip subsequent calls.
Note: Using the return
statement in the body
closure will only
exit from the current call to body
, not any outer scope, and won't
skip subsequent calls.
Complexity: O(self.count
)
Declaration
func forEach(@noescape body: (Self.Generator.Element) throws -> Void) rethrows
Declared In
SequenceType
Returns true
iff self
precedes other
in a lexicographical
("dictionary") ordering, using isOrderedBefore
as the comparison
between elements.
Note: This method implements the mathematical notion of lexicographical
ordering, which has no connection to Unicode. If you are sorting strings
to present to the end-user, you should use String
APIs that perform
localized comparison.
Requires: isOrderedBefore
is a
strict weak ordering
over the elements of self
and other
.
Declaration
func lexicographicalCompare<OtherSequence : SequenceType where OtherSequence.Generator.Element == Generator.Element>(other: OtherSequence, @noescape isOrderedBefore: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Bool
Declared In
SequenceType
Returns a LazyMapSequence
over this Sequence
. The elements of
the result are computed lazily, each time they are read, by
calling transform
function on a base element.
Declaration
func map<U>(transform: (Self.Elements.Generator.Element) -> U) -> LazyMapSequence<Self.Elements, U>
Declared In
LazySequenceType
, SequenceType
Returns the maximum element in self
or nil
if the sequence is empty.
Complexity: O(elements.count
).
Requires: isOrderedBefore
is a
strict weak ordering
over self
.
Declaration
func maxElement(@noescape isOrderedBefore: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element?
Declared In
SequenceType
Returns the minimum element in self
or nil
if the sequence is empty.
Complexity: O(elements.count
).
Requires: isOrderedBefore
is a
strict weak ordering
over self
.
Declaration
func minElement(@noescape isOrderedBefore: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element?
Declared In
SequenceType
Returns the result of repeatedly calling combine
with an
accumulated value initialized to initial
and each element of
self
, in turn, i.e. return
combine(combine(...combine(combine(initial, self[0]),
self[1]),...self[count-2]), self[count-1])
.
Declaration
func reduce<T>(initial: T, @noescape combine: (T, Self.Generator.Element) throws -> T) rethrows -> T
Declared In
SequenceType
Returns an Array
containing the elements of self
in reverse
order.
Complexity: O(N), where N is the length of self
.
Declaration
func reverse() -> [Self.Generator.Element]
Declared In
SequenceType
Returns an Array
containing the sorted elements of source
according to isOrderedBefore
.
The sorting algorithm is not stable (can change the relative order of
elements for which isOrderedBefore
does not establish an order).
Requires: isOrderedBefore
is a
strict weak ordering
over the elements in self
.
Declaration
func sort(@noescape isOrderedBefore: (Self.Generator.Element, Self.Generator.Element) -> Bool) -> [Self.Generator.Element]
Declared In
SequenceType
Returns the maximal SubSequence
s of self
, in order, that
don't contain elements satisfying the predicate isSeparator
.
maxSplit
: The maximum number of SubSequence
s to
return, minus 1.
If maxSplit + 1
SubSequence
s are returned, the last one is
a suffix of self
containing the remaining elements.
The default value is Int.max
.
allowEmptySubsequences
: If true
, an empty SubSequence
is produced in the result for each pair of consecutive elements
satisfying isSeparator
.
The default value is false
.
Requires: maxSplit >= 0
Declaration
func split(maxSplit: Int = default, allowEmptySlices: Bool = default, @noescape isSeparator: (Self.Generator.Element) throws -> Bool) rethrows -> [AnySequence<Self.Generator.Element>]
Declared In
SequenceType
Returns true
iff self
begins with elements equivalent to those of
other
, using isEquivalent
as the equivalence test. Returns true
if
other
is empty.
Requires: isEquivalent
is an
equivalence relation.
Declaration
func startsWith<OtherSequence : SequenceType where OtherSequence.Generator.Element == Generator.Element>(other: OtherSequence, @noescape isEquivalent: (Self.Generator.Element, Self.Generator.Element) throws -> Bool) rethrows -> Bool
Declared In
SequenceType
Returns a slice, up to maxLength
in length, containing the
final elements of s
.
If maxLength
exceeds s.count
, the result contains all
the elements of s
.
Requires: self
is a finite sequence.
Requires: maxLength >= 0
Declaration
func suffix(maxLength: Int) -> AnySequence<Self.Generator.Element>
Declared In
SequenceType
Returns a value less than or equal to the number of elements in
self
, nondestructively.
Complexity: O(N).
Declaration
func underestimateCount() -> Int
Declared In
SequenceType
Where Elements == Self
Where Elements.Generator.Element == Generator.Element, Generator.Element : SequenceType
A concatenation of the elements of self
.
Declaration
func flatten() -> LazySequence<FlattenSequence<Self.Elements>>
Where Generator == Self, Self : GeneratorType
Returns a generator over the elements of this sequence.
Complexity: O(1).
Declaration
func generate() -> Self
Declared In
SequenceType
Where Generator.Element : Comparable
Returns true
iff self
precedes other
in a lexicographical
("dictionary") ordering, using "<" as the comparison between elements.
Note: This method implements the mathematical notion of lexicographical
ordering, which has no connection to Unicode. If you are sorting strings
to present to the end-user, you should use String
APIs that perform
localized comparison.
Declaration
func lexicographicalCompare<OtherSequence : SequenceType where OtherSequence.Generator.Element == Generator.Element>(other: OtherSequence) -> Bool
Declared In
SequenceType
Returns the maximum element in self
or nil
if the sequence is empty.
Complexity: O(elements.count
).
Declaration
func maxElement() -> Self.Generator.Element?
Declared In
SequenceType
Returns the minimum element in self
or nil
if the sequence is empty.
Complexity: O(elements.count
).
Declaration
func minElement() -> Self.Generator.Element?
Declared In
SequenceType
Returns an Array
containing the sorted elements of source
.
The sorting algorithm is not stable (can change the relative order of elements that compare equal).
Requires: The less-than operator (func <
) defined in
the Comparable
conformance is a
strict weak ordering
over the elements in self
.
Declaration
func sort() -> [Self.Generator.Element]
Declared In
SequenceType
Where Generator.Element : Equatable
Returns true
iff element
is in self
.
Declaration
func contains(element: Self.Generator.Element) -> Bool
Declared In
SequenceType
Returns true
iff self
and other
contain the same elements in the
same order.
Declaration
func elementsEqual<OtherSequence : SequenceType where OtherSequence.Generator.Element == Generator.Element>(other: OtherSequence) -> Bool
Declared In
SequenceType
Returns the maximal SubSequence
s of self
, in order, around elements
equatable to separator
.
maxSplit
: The maximum number of SubSequence
s to
return, minus 1.
If maxSplit + 1
SubSequence
s are returned, the last one is
a suffix of self
containing the remaining elements.
The default value is Int.max
.
allowEmptySubsequences
: If true
, an empty SubSequence
is produced in the result for each pair of consecutive elements
satisfying isSeparator
.
The default value is false
.
Requires: maxSplit >= 0
Declaration
func split(separator: Self.Generator.Element, maxSplit: Int = default, allowEmptySlices: Bool = default) -> [AnySequence<Self.Generator.Element>]
Declared In
SequenceType
Returns true
iff the initial elements of self
are equal to prefix
.
Returns true
if other
is empty.
Declaration
func startsWith<OtherSequence : SequenceType where OtherSequence.Generator.Element == Generator.Element>(other: OtherSequence) -> Bool
Declared In
SequenceType
Where Generator.Element : SequenceType
A concatenation of the elements of self
.
Declaration
func flatten() -> FlattenSequence<Self>
Declared In
SequenceType
Returns a view, whose elements are the result of interposing a given
separator
between the elements of the sequence self
.
For example,
[[1, 2, 3], [4, 5, 6], [7, 8, 9]].joinWithSeparator([-1, -2])
yields [1, 2, 3, -1, -2, 4, 5, 6, -1, -2, 7, 8, 9]
.
Declaration
func joinWithSeparator<Separator : SequenceType where Separator.Generator.Element == Generator.Element.Generator.Element>(separator: Separator) -> JoinSequence<Self>
Declared In
SequenceType
Where Generator.Element == String
Interpose the separator
between elements of self
, then concatenate
the result. For example:
["foo", "bar", "baz"].joinWithSeparator("-|-") // "foo-|-bar-|-baz"
Declaration
func joinWithSeparator(separator: String) -> String
Declared In
SequenceType
Where SubSequence : SequenceType, SubSequence.Generator.Element == Generator.Element, SubSequence.SubSequence == SubSequence
Returns a subsequence containing all but the first n
elements.
Requires: n >= 0
Complexity: O(n
)
Declaration
func dropFirst(n: Int) -> AnySequence<Self.Generator.Element>
Declared In
SequenceType
Returns a subsequence containing all but the last n
elements.
Requires: self
is a finite collection.
Requires: n >= 0
Complexity: O(self.count
)
Declaration
func dropLast(n: Int) -> AnySequence<Self.Generator.Element>
Declared In
SequenceType
Returns a subsequence, up to maxLength
in length, containing the
initial elements.
If maxLength
exceeds self.count
, the result contains all
the elements of self
.
Requires: maxLength >= 0
Declaration
func prefix(maxLength: Int) -> AnySequence<Self.Generator.Element>
Declared In
SequenceType
A sequence on which normally-eager operations such as
map
andfilter
are implemented lazily.Lazy sequences can be used to avoid needless storage allocation and computation, because they use an underlying sequence for storage and compute their elements on demand. For example,
is a sequence containing {
2
,4
,6
}. Each time an element of the lazy sequence is accessed, an element of the underlying array is accessed and transformed by the closure.Sequence operations taking closure arguments, such as
map
andfilter
, are normally eager: they use the closure immediately and return a new array. Using thelazy
property gives the standard library explicit permission to store the closure and the sequence in the result, and defer computation until it is needed.To add new lazy sequence operations, extend this protocol with methods that return lazy wrappers that are themselves
LazySequenceType
s. For example, given an eagerscan
method defined as followswe can build a sequence that lazily computes the elements in the result of
scan
:and finally, we can give all lazy sequences a lazy
scan
method:See Also:
LazySequence
,LazyCollectionType
,LazyCollection
Note: The explicit permission to implement further operations lazily applies only in contexts where the sequence is statically known to conform to
LazySequenceType
. Thus, side-effects such as the accumulation ofresult
below are never unexpectedly dropped or deferred:[We don't recommend that you use
map
this way, because it creates and discards an array.sum
would be better implemented usingreduce
].