Iterators: Difference between revisions
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→{{header|Raku}}: Expand verbiage a bit, contrast explicit iterators with object slice notation
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=={{header|Raku}}==
Raku has iterators, but is rare for casual users to ever
Rakus iterators are one direction only (not reversible),
Once an iteration has been reified, it is discarded unless explicitly cached. This allows effortless iteration through multi-gigabyte sized data objects and streams without filling up main memory.
The following example iterates though a hash of Positional Iterable objects and demonstrates object slice operations on each; then has a semi contrived example of where directly using iterators may be actually useful in Raku; collating unique ascending values from several infinite sequence generators. ▼
▲The following example iterates though a hash of Positional Iterable objects and demonstrates both using explicit iterators, and object slice operations on each; then has a semi contrived example of where directly using iterators may be actually useful in Raku; collating unique ascending values from several infinite sequence generators.
<lang perl6>my %positional-iterable-types =
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;
sub first-fourth-fifth ($iterable) {
my $iterator = $iterable.iterator;
gather {
take $iterator.pull-one;
$iterator.pull-one xx 2;
take $iterator.pull-one;
take $iterator.pull-one;
}
}
say "Note: here we are iterating over the %positional-iterable-types hash, but
the order we get elements out is not the same as the order they were inserted.
Hashes are not guaranteed to be in any specific order, in fact, they are
guaranteed to _not_ be in any specific order.";
for %positional-iterable-types.values {
say "\nType " ~ .^name ~ ', contents: ' ~ $_
"\nUsing object slices: first, fourth and fifth from start: " ~ .[0, 3, 4] ~ ', and from end: ' ~ .[*-1, *-4, *-5] ~ "\n";
};
say "\nWhere iterators really shine; when you are
my @i = (1, * × 2 … *).iterator, (1, * × 3 … *).iterator, (1, * × 5 … *).iterator;
my @v = @i[0].pull-one, @i[1].pull-one, @i[2].pull-one;
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Hashes are not guaranteed to be in any specific order, in fact, they are
guaranteed to _not_ be in any specific order.
Type List, contents: Red Orange Yellow Green Blue Purple▼
First, fourth and fifth from start; Red Green Blue, and from end: Purple Yellow Orange▼
Type Range, contents: Rako Rakp Rakq Rakr Raks Rakt Raku Rakv Rakw Rakx Raky
Using object slices: first, fourth and fifth from start: Rako Rakr Raks, and from end: Raky Rakv Raku
Type Array, contents: Sunday Monday Tuesday Wednesday Thursday Friday Saturday▼
First, fourth and fifth from start; Sunday Wednesday Thursday, and from end: Saturday Wednesday Tuesday▼
Type Seq, contents: 1.25 1.5 1.875 2.8125 5.273438 14.831543 78.2132149
Using object slices: first, fourth and fifth from start: 1.25 2.8125 5.273438, and from end: 78.2132149 2.8125 1.875
▲Type Array, contents: Sunday Monday Tuesday Wednesday Thursday Friday Saturday
▲
Using object slices: first, fourth and fifth from start: Sunday Wednesday Thursday, and from end: Saturday Wednesday Tuesday
▲Type List, contents: Red Orange Yellow Green Blue Purple
▲
Using object slices: first, fourth and fifth from start: Red Green Blue, and from end: Purple Yellow Orange
Where iterators really shine; when you are
(1 2 3 4 5 8 9 16 25 27 32 64 81 125 128 243 256 512 625 729 1024 2048 2187 3125 4096)</pre>
=={{header|Wren}}==
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