rfc:cachediterable

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rfc:cachediterable [2021/02/11 03:00]
tandre benchmarks 		rfc:cachediterable [2021/06/15 13:47]
tandre
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-====== PHP RFC: CachedIterable (rewindable, allows any key&repeating keys)  ====== +====== PHP RFC: ImmutableIterable (immutable, rewindable, memory-efficient, allows any key&repeating keys)  ====== 
-  * Version: 0.1+  * Version: 0.4
   * Date: 2021-02-06   * Date: 2021-02-06
   * Author: Tyson Andre, tandre@php.net   * Author: Tyson Andre, tandre@php.net
-  * Status: Draft+  * Status: Voting
   * Implementation: https://github.com/php/php-src/pull/6655   * Implementation: https://github.com/php/php-src/pull/6655
   * First Published at: https://wiki.php.net/rfc/cachediterable   * First Published at: https://wiki.php.net/rfc/cachediterable
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   - Creating a rewindable copy of a non-rewindable Traversable (e.g. a ''Generator'') before passing that copy to a function that consumes an iterable/Traversable. (''new CachedIterator(my_generator())'')   - Creating a rewindable copy of a non-rewindable Traversable (e.g. a ''Generator'') before passing that copy to a function that consumes an iterable/Traversable. (''new CachedIterator(my_generator())'')
-  - Generating an ''IteratorAggregate'' from a class still implementing ''Iterator'' (e.g. ''SplObjectStorage'') so that code can independently iterate over the key-value sequences. \\ (e.g. ''foreach ($cachingIterable as $k1 => $v1) { foreach ($cachingIterable as $k2 => $v2) { /* process pairs */ } }'')+  - Generating an ''IteratorAggregate'' from a class still implementing ''Iterator'' (e.g. ''SplObjectStorage'') so that code can independently iterate over the key-value sequences. \\ (e.g. ''foreach ($immutableKeyValueSequence as $k1 => $v1) { foreach ($immutableKeyValueSequence as $k2 => $v2) { /* process pairs */ } }'')
   - Providing internal or userland helpers such as ''iterable_flip(iterable $input)'', ''iterable_take(iterable $input, int $limit)'', ''iterable_chunk(iterable $input, int $chunk_size)'' that act on iterables with arbitrary key/value sequences and have return values including iterables with arbitrary key/value sequences   - Providing internal or userland helpers such as ''iterable_flip(iterable $input)'', ''iterable_take(iterable $input, int $limit)'', ''iterable_chunk(iterable $input, int $chunk_size)'' that act on iterables with arbitrary key/value sequences and have return values including iterables with arbitrary key/value sequences
-  - Providing memory-efficient random access to both keys and values of arbitrary key-value sequences (for binary searching on keys and/or values, etc.)+  - Providing constant time access to both keys and values of arbitrary key-value sequences at any offset (for binary searching on keys and/or values, etc.) 
 + 
 +Having this implemented as an internal class would also allow it to be [[#benchmarks|much more efficient than a userland solution]] (in terms of time to create, time to iterate over the result, and total memory usage).
  
 ===== Proposal ===== ===== Proposal =====
  
-Add a class ''CachedIterable'' that contains an immutable copy of the keys and values of the iterable it was constructed from. (references inside of arrays within those keys/values will remain modifiable references, and objects within those keys/values will remain mutable)+Add a class ''ImmutableIterable'' that contains an immutable copy of the keys and values of the iterable it was constructed from. (references inside of arrays within those keys/values will remain modifiable references, and objects within those keys/values will remain mutable)
  
 <code php> <code php>
-final class CachedIterable implements IteratorAggregate, Countable, JsonSerializable+final class ImmutableIterable implements  
 +    IteratorAggregate, 
 +    Countable, 
 +    JsonSerializable 
 { {
     public function __construct(iterable $iterator) {}     public function __construct(iterable $iterator) {}
Line 27: Line 32:
     public function count(): int {}     public function count(): int {}
     // [[$key1, $value1], [$key2, $value2]]     // [[$key1, $value1], [$key2, $value2]]
-    public static function fromPairs(array $pairs): CachedIterable {}+    public static function fromPairs(array $pairs): ImmutableIterable {}
     // [[$key1, $value1], [$key2, $value2]]     // [[$key1, $value1], [$key2, $value2]]
-    public function toPairs(): array{} +    public function toPairs(): array{}
     public function __serialize(): array {}  // [$k1, $v1, $k2, $v2,...]     public function __serialize(): array {}  // [$k1, $v1, $k2, $v2,...]
     public function __unserialize(array $data): void {}     public function __unserialize(array $data): void {}
 +    public static function __set_state(array $array): ImmutableIterable {}
  
     // useful for converting iterables back to arrays for further processing     // useful for converting iterables back to arrays for further processing
Line 39: Line 45:
     public function keyAt(int $offset): mixed {}     public function keyAt(int $offset): mixed {}
     public function valueAt(int $offset): mixed {}     public function valueAt(int $offset): mixed {}
-    +
     // '[["key1","value1"],["key2","value2"]]' instead of '{...}'     // '[["key1","value1"],["key2","value2"]]' instead of '{...}'
     public function jsonSerialize(): array {}     public function jsonSerialize(): array {}
Line 46: Line 52:
 </code> </code>
  
-CachedIterables are IteratorAggregates, so foreach loops do not interfere with each other.+ImmutableIterables are IteratorAggregates, so foreach loops do not interfere with each other.
  
 <code php> <code php>
-$x = new CachedIterable([0 => 100, 'key' => 'value']);+$x = new ImmutableIterable([0 => 100, 'key' => 'value']);
 foreach ($x as $key1 => $value1) { foreach ($x as $key1 => $value1) {
     echo "$key1 $value1:\n";     echo "$key1 $value1:\n";
Line 66: Line 72:
 </code> </code>
  
-==== CachedIterables can be used to cache and efficiently process results of Traversables ====+==== ImmutableIterables can be used to cache and efficiently process results of Traversables ====
  
-CachedIterables can be created from any iterable (arrays or Traversables). They eagerly evaluate the results of Traversables (e.g. Generators) and store an exact copy of the keys and values that can be processed in many ways.+ImmutableIterables can be created from any iterable (arrays or Traversables). They eagerly evaluate the results of Traversables (e.g. Generators) and store an exact copy of the keys and values that can be processed in many ways. 
 + 
 +In comparison to php's ''array''/''ArrayObject'' type: 
 + 
 +  * Arrays can only store integers and strings 
 +  * Arrays coerce stringified integers to integers, potentially causing unexpected Errors/notices (especially when ''strict_types=1'') 
 +  * Arrays cannot represent repeated keys
  
 <code php> <code php>
Line 79: Line 91:
 } }
  
-$x = new CachedIterable(my_generator());+$x = new ImmutableIterable(my_generator());
 foreach ($x as $k => $v) { foreach ($x as $k => $v) {
     printf("%s: %s\n", json_encode($k), json_encode($v));     printf("%s: %s\n", json_encode($k), json_encode($v));
Line 101: Line 113:
 </code> </code>
  
-==== CachedIterables are immutable ====+==== ImmutableIterables are immutable ====
  
-CachedIterable is a final class.+ImmutableIterable is a final class.
  
-Dynamic properties are forbidden on CachedIterables.+Dynamic properties are forbidden on ImmutableIterables.
  
-The keys and values of the CachedIterable cannot be modified or appended to after an instance is constructed, though objects and references within those values can be modified.+The keys and values of the ImmutableIterable cannot be modified or appended to after an instance is constructed, though objects and references within those values can be modified.
  
-==== CachedIterables can be created from pairs ====+This makes it useful for returning to wrap the keys and values that would be returned by a generator or single-use ''Iterator'' (it can't be modified after being constructed by other applications or libraries) 
 + 
 +==== ImmutableIterables can be created from pairs ====
  
 This can be done imperatively, to avoid the need to manually create a generator with the sequence of keys and values to pass to the constructor. The values of an iterable (array or Traversable) can be used. This can be done imperatively, to avoid the need to manually create a generator with the sequence of keys and values to pass to the constructor. The values of an iterable (array or Traversable) can be used.
  
 <code php> <code php>
-$it = CachedIterable::fromPairs([['first', 'x'], [(object)['key' => 'value'], null]]);+$it = ImmutableIterable::fromPairs([['first', 'x'], [(object)['key' => 'value'], null]]);
 foreach ($it as $key => $value) { foreach ($it as $key => $value) {
     printf("key=%s value=%s\n", json_encode($key), json_encode($value));     printf("key=%s value=%s\n", json_encode($key), json_encode($value));
Line 124: Line 138:
 var_dump($it); var_dump($it);
 /* /*
-object(CachedIterable)#2 (1) {+object(ImmutableIterable)#2 (1) {
   [0]=>   [0]=>
   array(2) {   array(2) {
Line 138: Line 152:
 </code> </code>
  
-CachedIterables can also be converted back into pairs for further processing (e.g. using the wide array of helper methods php has for processing arrays):+ImmutableIterables can also be converted back into pairs for further processing (e.g. using the wide array of helper methods php has for processing arrays):
  
 <code php> <code php>
-php > $reversedIt = CachedIterable::fromPairs(array_reverse($it->toPairs()));+php > $reversedIt = ImmutableIterable::fromPairs(array_reverse($it->toPairs()));
 php > echo json_encode($reversedIt->toPairs()); php > echo json_encode($reversedIt->toPairs());
 [[{"key":"value"},null],["first","x"]] [[{"key":"value"},null],["first","x"]]
 </code> </code>
  
-==== CachedIterables are memory-efficient ====+===== Benchmarks =====
  
-Similarly to how ''SplFixedArray'' is a memory-efficient way to store a list of values, ''CachedIterable'' is a memory-efficient way to store a sequence of keys and values (allowing repeated keys of any type).+==== ImmutableIterables are memory-efficient ==== 
 + 
 +Similarly to how ''SplFixedArray'' is a memory-efficient way to store a list of values, ''ImmutableIterable'' is a memory-efficient way to eagerly evaluate and store a sequence of arbitrary keys and values.
  
 <code php> <code php>
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     gc_collect_cycles();     gc_collect_cycles();
     $before = memory_get_usage();     $before = memory_get_usage();
-    $result = array_flip(range(10, 10 + $n - 1));+    $result = array_flip(range(10, 10 + $n - 1));  // create an **associative** array of size $n
     $after = memory_get_usage();     $after = memory_get_usage();
-    printf("array memory:          (n=%5d) %7d bytes\n", $n, $after - $before);+    printf("array memory:          (n=%5d) %7d bytes\n", count($result), $after - $before);
 } }
 function show_cachediterable_memory(int $n) { function show_cachediterable_memory(int $n) {
     gc_collect_cycles();     gc_collect_cycles();
     $before = memory_get_usage();     $before = memory_get_usage();
-    $result = new CachedIterable(array_flip(range(10, 10 + $n - 1)));+    // create a ImmutableIterable from an **associative** array of size $n 
 +    $result = new ImmutableIterable(array_flip(range(10, 10 + $n - 1)));
     $after = memory_get_usage();     $after = memory_get_usage();
-    printf("CachedIterable memory: (n=%5d) %7d bytes\n", $n, $after - $before);+    printf("ImmutableIterable memory: (n=%5d) %7d bytes\n", count($result), $after - $before);
 } }
 foreach ([1, 8, 12, 16, 2**16] as $n) { foreach ([1, 8, 12, 16, 2**16] as $n) {
Line 172: Line 189:
 } }
 /* /*
-array memory:          (n=    1)     480 bytes +array memory:             (n=    1)     376 bytes 
-CachedIterable memory: (n=    1)     160 bytes +ImmutableIterable memory: (n=    1)      88 bytes 
-array memory:          (n=    8)     480 bytes +array memory:             (n=    8)     376 bytes 
-CachedIterable memory: (n=    8)     416 bytes +ImmutableIterable memory: (n=    8)     312 bytes 
-array memory:          (n=   12)    1632 bytes +array memory:             (n=   12)    1336 bytes 
-CachedIterable memory: (n=   12)     544 bytes +ImmutableIterable memory: (n=   12)     440 bytes 
-array memory:          (n=   16)    1632 bytes +array memory:             (n=   16)    1336 bytes 
-CachedIterable memory: (n=   16)     736 bytes +ImmutableIterable memory: (n=   16)     568 bytes 
-array memory:          (n=65536) 4198592 bytes +array memory:             (n=65536) 4198480 bytes 
-CachedIterable memory: (n=65536) 2097344 bytes+ImmutableIterable memory: (n=65536) 2097232 bytes
  */  */
 </code> </code>
  
-==== CachedIterables are much more efficient than a polyfill ====+==== ImmutableIterables are much more efficient than a polyfill object ====
  
-For a simple example, this uses much less time to construct. It is also 6 times faster to iterate over and process results than a polyfill, and uses half as much additional memory.+For a simple example, this uses much less time to construct. It is almost 6 times faster to iterate over and process results than a polyfill in that example, and uses half as much additional memory.
  
 <code php> <code php>
 <?php <?php
 /* /*
-Time to construct PolyfillIterator: 0.246372, Time to iterate: 0.617741, result 999000000, memory usage: 67117600 +Time to construct PolyfillImmutableIterator: 0.244787 
-Time to construct   CachedIterable: 0.130583, Time to iterate: 0.095657, result 999000000, memory usage: 32002240+Time to iterate: 0.183351, memory usage: 67117328 
 +result:999000000 
 + 
 +Time to construct         ImmutableIterable: 0.130534 
 +Time to iterate: 0.021905, memory usage: 32002128 
 +result:999000000
  */  */
  
-// Not an IteratorAggregate for simplicity but still rewindable - unimportant to performance +/** 
-class PolyfillIterator implements Iterator {+ * THIS IS AN INCOMPLETE POLYFILL THAT ONLY SUPPORTS ITERATION, AND DOES NOT INCLUDE ERROR HANDLING. 
 + * 
 + * Barely any of the functionality in the proposal is implemented. 
 + * This is just here to compare a fast (in terms of time to iterate) userland polyfill 
 + * against ImmutableIterable. 
 + * 
 + * Not an IteratorAggregate for simplicity. 
 + */ 
 +class PolyfillImmutableIterator implements Iterator {
     public $i = 0;     public $i = 0;
     public $count = 0;     public $count = 0;
Line 241: Line 271:
     gc_collect_cycles();     gc_collect_cycles();
     $memory_usage_2 = memory_get_usage();     $memory_usage_2 = memory_get_usage();
-    printf("Time to construct %16s: %.6f, Time to iterate: %.6f, result %d, memory usage: %d\n", +    printf("Time to construct %25s: %.6f\nTime to iterate: %.6f, memory usage: %d\nresult:%d\n\n", 
-        $class, $t2 - $t1, $t3 - $t2, $total, $memory_usage_2 - $memory_usage_1);+        $class, $t2 - $t1, $t3 - $t2, $memory_usage_2 - $memory_usage_1, $total);
 } }
-benchmark(PolyfillIterator::class); +benchmark(PolyfillImmutableIterator::class); 
-benchmark(CachedIterable::class); +benchmark(ImmutableIterable::class);
 </code> </code>
-==== CachedIterables support constant-time access to keys and values ====+==== ImmutableIterables support constant-time access to keys and values ====
  
-CachedIterables support constant-time access to keys and values, allowing the result to be used in a wide variety of ways in an applicat.+''ImmutableIterable''s support constant-time access to keys and values, allowing the result to be used in a wide variety of ways in an application.
 For example, it is possible to do binary search on keys (and/or values) without using any additional time or memory to create a copy of the keys. For example, it is possible to do binary search on keys (and/or values) without using any additional time or memory to create a copy of the keys.
 (Same for values). (Same for values).
Line 260: Line 289:
  * Returns count($it) if all keys are smaller than $target.  * Returns count($it) if all keys are smaller than $target.
  */  */
-function do_binary_search_on_key(CachedIterable $it, int $target) {+function do_binary_search_on_key(ImmutableIterable $it, int $target) {
     $lowOffset = 0;     $lowOffset = 0;
     $highOffset = count($it) - 1;     $highOffset = count($it) - 1;
Line 274: Line 303:
         }         }
     }     }
-    echo "offset $lowOffset has the first key ({$it->keyAt($lowOffset)}) >= $target : associated value={$it->valueAt($lowOffset)}\n";+    echo "offset $lowOffset has the first key ({$it->keyAt($lowOffset)}) >= $target " . 
 +         ": associated value={$it->valueAt($lowOffset)}\n";
     return $lowOffset;     return $lowOffset;
 } }
Line 285: Line 315:
 } }
 ksort($data); ksort($data);
-$it = new CachedIterable($data);+$it = new ImmutableIterable($data);
  
 do_binary_search_on_key($it, mt_rand()); do_binary_search_on_key($it, mt_rand());
Line 304: Line 334:
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
-None, except that the class name ''CachingIterable'' will be declared by PHP and conflict with applications declaring the same class name in that namespace.+None, except that the class name ''ImmutableIterable'' will be declared by PHP and conflict with applications declaring the same class name in that namespace.
  
 ===== Proposed PHP Version(s) ===== ===== Proposed PHP Version(s) =====
Line 311: Line 341:
 ===== Future Scope ===== ===== Future Scope =====
  
-  * This will enable adding internal iterable functions such as ''PHP\iterable\take(iterable $input, int $limit): CachingIterator'' or ''PHP\iterable\flip(iterable $input): CachingIterator'' +  * This will enable adding internal iterable functions such as ''*take(iterable $input, int $limit): ImmutableIterable'' or ''*flip(iterable $input): ImmutableIterable'' or 
-  * More methods may be useful to add to CachingIterable, e.g. for returning a sorted copy, returning a slice(range of entries), returning a copy sorted by keys/values, quickly returning the index/corresponding value of the first occurrence of ''mixed $key'' etc. +  * More methods may be useful to add to ''ImmutableIterable'', e.g. for returning a sorted copy, returning a slice(range of entries), returning a copy sorted by keys/values, quickly returning the index/corresponding value of the first occurrence of ''mixed $key'' etc. 
-  * This may or may not be useful for future data types, e.g. a MapObject (hash map on any key type) type and may potentially be useful for converting some existing internal/user-defined Iterable types to IteratorAggregate types.+  * This may or may not be useful for future data types, e.g. a ''MapObject'' (hash map on any key type) type and may potentially be useful for converting some existing internal/user-defined ''Iterable'' types to ''IteratorAggregate'' types. 
 +    * A new ''IterableAggregate'' subclass such as ''CachedIterator''/''CachedIterable'' could be added to compute values [[https://en.wikipedia.org/wiki/Lazy_evaluation|lazily(on-demand)]] in contrast to ''ImmutableIterable'', which [[https://en.wikipedia.org/wiki/Eager_evaluation|evaluates the entire iterable in the constructor]].
  
-===== Proposed Voting Choices ===== +===== Vote ===== 
-Yes/No, requiring a 2/3 majority.+This is a Yes/No vote, requiring a 2/3 majority. Voting started on June 15, 2021 and ends on June 29, 2021. 
 + 
 +<doodle title="Add ImmutableIterable to core" auth="tandre" voteType="single" closed="false"> 
 +   * Yes 
 +   * No 
 +</doodle> 
 + 
 +==== Poll: Reason for voting against this RFC ==== 
 + 
 +<doodle title="Reasons for voting against the ImmutableIterable RFC" auth="tandre" voteType="multi" closed="false"> 
 +   * Object to the namespace choice 
 +   * Object to the name 
 +   * Object to the implementation 
 +   * Don't see a use case 
 +   * Other 
 +</doodle>
  
 ===== References ===== ===== References =====
  
-[[https://externals.io/message/113061#113066|Proposal: Add ReverseArrayIterator and ForwardArrayIterator to SPL]]+  * [[https://externals.io/message/113061#113066|Proposal: Add ReverseArrayIterator and ForwardArrayIterator to SPL]] 
 +  * [[rfc:cachediterable_straw_poll|Straw poll: Namespace to use for CachedIterable and iterable functionality]] 
 +  * https://externals.io/message/114834  RFC: CachedIterable (rewindable, allows any key&repeating keys)
  
 ===== Rejected Features ===== ===== Rejected Features =====
 +
 +==== Rejected: Alternative namespaces ====
 +
 +[[rfc:cachediterable_straw_poll|Straw poll: Namespace to use for CachedIterable and iterable functionality]] did not indicate a majority of voters preferred alternative namespace choices for a namespace over not using a namespace for newly added caches. This chooses the global namespace to maintain consistency with existing spl classes and interfaces.
 +
  
 ==== Rejected: ArrayAccess ==== ==== Rejected: ArrayAccess ====
Line 330: Line 383:
 I think ''ArrayAccess'' would lead to more bugs in application code for those expecting ''$cachedIt[$i]'' to find the value corresponding to the first key occurrence of ''$i'' - adding ''keyAt(int $offset): mixed'', ''valueAt(int $offset): mixed'', ''keyIndex(mixed $key): int'', ''valueIndex(mixed $value): int'' would be my preference for fetching values. I think ''ArrayAccess'' would lead to more bugs in application code for those expecting ''$cachedIt[$i]'' to find the value corresponding to the first key occurrence of ''$i'' - adding ''keyAt(int $offset): mixed'', ''valueAt(int $offset): mixed'', ''keyIndex(mixed $key): int'', ''valueIndex(mixed $value): int'' would be my preference for fetching values.
 </blockquote> </blockquote>
 +
 +==== Rejected: Lazy Evaluation ====
 +
 +''ImmutableIterable'' evaluates the entire iterable in its constructor ([[https://en.wikipedia.org/wiki/Eager_evaluation|eagerly]] instead of [[https://en.wikipedia.org/wiki/Lazy_evaluation|lazily]]) for the following reasons:
 +
 +  * If this is generated from a data structure, the behavior may be unintuitive if the underlying data is modified while iterating over the sequence of keys and values if this were to be evaluated lazily instead of eagerly.
 +  * Evaluating the entire iterable in the constructor ensures that exceptions will be thrown during construction instead of during iteration or call to count()/keyAt()/valueAt() - it would be unintuitive for those iteration methods to throw ''SomeUserlandFrameworkException''
 +  * This is easier to understand, debug, serialize, and represent
 +  * If the underlying iterable (e.g. a Generator) has side effects, having those side effects take place immediately instead of being interleaved with other parts of the program may be easier to reason about.
 +  * The majority of use cases of ''Traversable''s would iterate over the entire Traversable at some point.
 +  * Eagerly evaluating iterables reduces the memory needed by the implementation. The amount of memory needed to represent this is much lower (without the need to store the underlying iterable, potentially the most recent exception(s) thrown by the undlying iterable, etc).
 +
 +
 +The addition of an iterable library class that evaluates arguments on-demand is mentioned in the "future scope" section.
 +
 +https://externals.io/message/114805#114798
 +
 +<blockquote>
 +<blockquote>
 +2) Userland library/application authors that are interested in lazy generators could use or implement something
 +such as https://github.com/nikic/iter instead. My opinion is that the standard library should provide
 +something that is easy to understand, debug, serialize or represent, etc.
 +I expect the inner iterable may be hidden entirely in a (lazy) CachedIterable from var_dump as an implementation detail.
 +
 +3) It would be harder to understand why SomeFrameworkException is thrown in code unrelated to that framework
 +when a lazy (instead of eager) iterable is passed to some function that accepts a generic iterable,
 +and harder to write correct exception handling for it if done in a lazy generation style.
 +
 +Many RFCs have been rejected due to being perceived as being likely to be misused in userland or
 +to make code harder to understand.
 +
 +4) It is possible to implement a lazy alternative to (ImmutableIterable) that only loads values as needed.
 +However, I hadn't proposed it due to doubts that 2/3 of voters would consider it widely useful
 +enough to be included in php rather than as a userland or PECL library.
 +</blockquote>
 +
 +CachedIterable should load from the underlying
 +datastore lazily -- there is hardly any visible impact from the user
 +if this happens, because for the most part it looks and behaves the
 +same as it does today. The only visible changes are around loading
 +data from the underlying iterable.
 +
 +For example, if the user calls the count method on the CachedIterable,
 +it would then load the remainder of the underlying data-store (and
 +then drop its reference to it). If the user asks for valueAt($n) and
 +it's beyond what's already loaded and we haven't finished consuming
 +the underlying iterable, then it would load until $n is found or the
 +end of the store is reached.
 +
 +I understand your concerns with map, filter, etc. CachedIterable
 +is different because it holds onto the data, can be iterated over more
 +than once, including the two nested loop cases, even if it loads data
 +from the underlying iterable on demand.
 +</blockquote>
 +
 +<blockquote>
 +<blockquote>
 +Thanks for explaining 4 months ago about my concern.
 +I think I understand the main real impact of an eager iterable cache vs a lazy iterable cache from a functional point of view:
 +
 +  * exceptions are thrown during construction vs during the first iteration
 +  * predictable performance also on the first iteration.
 +
 +How did you gather the information that eager implementation is more valuable than lazy one? I'm mostly curious also how to assess this as technically to me it also looks the other way around. Maybe mention that in the RFC.
 +I was even thinking that CachedIterable should be lazy and an EagerCachedIterable would be built upon that with more methods. Or have it in the same class with a constructor parameter.
 +</blockquote>
 +
 +One of the reasons was size/efficiency. Adding the functionality to support lazy evaluation would require extra properties to track internal state and extra checks at runtime,
 +point to the original iterable and the functions being applied to that iterable - so an application that creates lots of small/empty cached iterables would have a higher memory usage.
 +
 +Having a data structure that tries to do everything would do other things poorly
 +(potentially not support serialization, use more memory than necessary,
 +have unintuitive behaviors when attempting to var_export/var_dump it,
 +surprisingly throw when being iterated over, etc)
 +</blockquote>
 +
 +==== Changelog ====
 +
 +  * 0.2: Use optimized build with opcache enabled for benchmark timings
 +  * 0.3: Rename from ''CachedIterable'' to ''ImmutableKeyValueSequence'' (the lack of clarity about the functionality associated with the name ''CachedIterable'' being eagerly evalulated was mentioned *after* most of the responses to the straw poll were already submitted). \\ Other names starting with ''Cached*'' were rejected for the same reason.
 +  * 0.3.1: Add ''__set_state''
 +  * 0.4.0: Rename from ''ImmutableKeyValueSequence'' to ''ImmutableIterable''
  
rfc/cachediterable.txt · Last modified: 2021/06/29 14:24 by tandre

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