# Pipelined filters and operations on iterators.
#
-# This module enhance `Iterator`s with some methods that enable a
-# pipeline-like programing that offers the manupulation of
-# collections trough connected filters with reasonable memory constraints.
+# This module enhances `Iterator` with some methods that enable a pipeline-like programing.
+# The processing of elements in a pipeline is done trough connected filters that are implemented with reasonable memory constraints.
module pipeline
redef interface Iterator[E]
# Filter: sort with a given `comparator`.
# Important: require O(n) memory.
- fun sort_with(comparator: Comparator[E]): Iterator[E]
+ #
+ # assert ["a", "c", "b"].iterator.sort_with(alpha_comparator).to_a == ["a", "b", "c"]
+ fun sort_with(comparator: Comparator): Iterator[E]
do
var a = self.to_a
comparator.sort(a)
#
# var i = [1,2,3,4,5].iterator
# assert i.head(2).to_a == [1,2]
- # i.to_a == [3,4,5]
+ # assert i.to_a == [3,4,5]
fun head(length: Int): Iterator[E]
do
return new PipeHead[E](self, length)
do
return new PipeSkipTail[E](self, length)
end
+
+ # Filter: reject items that does not meet some criteria.
+ #
+ # class IsEvenFunction
+ # super Function[Int, Bool]
+ # redef fun apply(i) do return i % 2 == 0
+ # end
+ # assert [1,2,3,4,8].iterator.select(new IsEvenFunction).to_a == [2,4,8]
+ fun select(predicate: Function[E, Bool]): Iterator[E]
+ do
+ return new PipeSelect[E](self, predicate)
+ end
+end
+
+# Wraps an iterator to skip nulls.
+#
+# ~~~nit
+# var i: Iterator[Int]
+#
+# i = new NullSkipper[Int]([null, 1, null, 2, null: nullable Int].iterator)
+# assert i.to_a == [1, 2]
+#
+# i = new NullSkipper[Int]([1, null, 2, 3: nullable Int].iterator)
+# assert i.to_a == [1, 2, 3]
+# ~~~
+class NullSkipper[E: Object]
+ super Iterator[E]
+
+ # The inner iterator.
+ var inner: Iterator[nullable E]
+
+ redef fun finish do inner.finish
+
+ redef fun is_ok do
+ skip_nulls
+ return inner.is_ok
+ end
+
+ redef fun item do
+ skip_nulls
+ return inner.item.as(E)
+ end
+
+ redef fun next do
+ inner.next
+ skip_nulls
+ end
+
+ private fun skip_nulls do
+ while inner.is_ok and inner.item == null do inner.next
+ end
+end
+
+# Interface that reify a function.
+# Concrete subclasses must implements the `apply` method.
+#
+# This interface helps to manipulate function-like objects.
+#
+# The main usage it as a transformation; that takes an argument and produce a result.
+# See `map` for example.
+#
+# Another usage is as a predicate, with `Function[E, Bool]`.
+# See `Iterator::select` for example.
+#
+# Function with more than one argument can be reified with some uncurification.
+# Eg. `Function[ARG1, Function[ARG2, RES]]`.
+#
+# NOTE: Nit is not a functionnal language, this class is a very basic way to
+# simulate the reification of a simple function.
+interface Function[FROM, TO]
+ # How an element is mapped to another one.
+ fun apply(e: FROM): TO is abstract
+
+ # Filter: produce an iterator which each element is transformed.
+ #
+ # var i = [1,2,3].iterator
+ # assert fun_to_s.map(i).to_a == ["1", "2", "3"]
+ #
+ # Note: because there is no generic method in Nit (yet?),
+ # there is no way to have a better API.
+ # eg. with the Iterator as receiver and the function as argument.
+ # (see `Iterator::select`)
+ fun map(i: Iterator[FROM]): Iterator[TO]
+ do
+ return new PipeMap[FROM, TO](i, self)
+ end
+end
+
+private class FunctionToS
+ super Function[Object, String]
+ redef fun apply(e) do return e.to_s
end
### Specific private iterator classes
var source: Iterator[E]
var skip_item: E
- init(source: Iterator[E], skip_item: E)
- do
- self.source = source
- self.skip_item = skip_item
-
- do_skip
- end
+ init do do_skip
fun do_skip
do
var lasts = new List[E]
- init(source: Iterator[E], length: Int)
+ init
do
- self.source = source
- self.length = length
var lasts = self.lasts
while source.is_ok and lasts.length < length do
lasts.push(source.item)
source.next
end
end
+
+private class PipeSelect[E]
+ super Iterator[E]
+
+ var source: Iterator[E]
+
+ var predicate: Function[E, Bool]
+
+ init do do_skip
+
+ fun do_skip
+ do
+ while source.is_ok and not predicate.apply(source.item) do source.next
+ end
+
+ redef fun is_ok do return source.is_ok
+
+ redef fun item do return source.item
+
+ redef fun next
+ do
+ source.next
+ do_skip
+ end
+end
+
+private class PipeMap[E, F]
+ super Iterator[F]
+
+ var source: Iterator[E]
+ var function: Function[E, F]
+
+ var item_cache: nullable F = null
+ var item_cached = false
+
+ redef fun is_ok do return source.is_ok
+
+ redef fun item do
+ if item_cached then return item_cache
+ item_cache = function.apply(source.item)
+ item_cached = true
+ return item_cache
+ end
+
+ redef fun next do
+ source.next
+ item_cached = false
+ end
+end
+
+# Stateless singleton that reify to the `to_s` method.
+#
+# assert fun_to_s.apply(5) == "5"
+fun fun_to_s: Function[Object, String] do return once new FunctionToS
nitlanguage / nit.git / blobdiff