c00d6ad694
This is a bit of a style preference since of course you can always write the same thing with a for loop. However, I think sometimes the code looks better when using this method. It also provides an alternative to Sequence.map for cases where you don't need the resulting list, and one that becomes especially necessary when Sequence.map is changed to return a new sequence. The example in the README.md file was using Sequence.map in a way that required this alternative in that case.
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^title Sequence Class ^category core
An abstract base class for any iterable object. Any class that implements the core iterator protocol can extend this to get a number of helpful methods.
Methods
all(predicate)
Tests whether all the elements in the sequence pass the predicate.
Iterates over the sequence, passing each element to the function predicate.
If its return value evaluates to false, stops iterating and returns false.
Otherwise, returns true.
:::dart
[1, 2, 3].all {|n| n > 2} // False.
[1, 2, 3].all {|n| n < 4} // True.
any(predicate)
Tests whether any element in the sequence passes the predicate.
Iterates over the sequence, passing each element to the function predicate.
If its return value evaluates to true, stops iterating and returns true.
Otherwise, returns false.
:::dart
[1, 2, 3].any {|n| n < 1} // False.
[1, 2, 3].any {|n| n > 2} // True.
contains(element)
Returns whether the sequence contains any element equal to the given element.
count
The number of elements in the sequence.
Unless a more efficient override is available, this will iterate over the sequence in order to determine how many elements it contains.
count(predicate)
Returns the number of elements in the sequence that pass the predicate.
Iterates over the sequence, passing each element to the function predicate
and counting the number of times the returned value evaluates to true.
:::dart
[1, 2, 3].count {|n| n > 2} // 1.
[1, 2, 3].count {|n| n < 4} // 3.
each(function)
Iterates over the sequence, passing each element to the given function.
:::dart
["one", "two", "three"].each {|word| IO.print(word) }
join(sep)
Returns a string representation of the list. The string representations of the
elements in the list is concatenated with intervening occurrences of sep.
It is a runtime error if sep is not a string.
join
Calls join with the empty string as the separator.
list
Creates a list containing all the elements in the sequence.
:::dart
(1..3).list // [1, 2, 3]
map(transformation)
Creates a new list by applying transformation to each element in the
sequence.
Iterates over the sequence, passing each element to the function
transformation. Generates a new list from the result of each of those calls.
:::dart
[1, 2, 3].map {|n| n * 2} // [2, 4, 6].
reduce(function)
Reduces the sequence down to a single value. function is a function that takes two arguments, the accumulator and sequence item and returns the new accumulator value. The accumulator is initialized from the first item in the sequence. Then, the function is invoked on each remaining item in the sequence, iteratively updating the accumulator.
It is a runtime error to call this on an empty sequence.
reduce(seed, function)
Similar to above, but uses seed for the initial value of the accumulator. If the sequence is empty, returns seed.
where(predicate)
Produces a new list containing only the elements in the sequence that pass the
predicate.
Iterates over the sequence, passing each element to the function predicate.
If it returns true, adds the element to the result list.
(1..10).where {|n| n % 2 == 1} // [1, 3, 5, 7, 9].