From b81939c238ecf43268e52e963d034943c2a0766a Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.com>
Date: Sat, 15 Apr 2023 09:40:50 +0900
Subject: [PATCH 1/6] Improve empty tracking

---
 src/Standard.php | 78 +++++++++++++++++++++++-------------------------
 1 file changed, 37 insertions(+), 41 deletions(-)

diff --git a/src/Standard.php b/src/Standard.php
index 8e1486a..beb1b1a 100644
--- a/src/Standard.php
+++ b/src/Standard.php
@@ -75,6 +75,11 @@ public function __construct(?iterable $input = null)
         $this->pipeline = $input;
     }
 
+    private function empty(): bool
+    {
+        return [] === $this->pipeline || null === $this->pipeline;
+    }
+
     /**
      * Appends the contents of an interable to the end of the pipeline.
      */
@@ -143,7 +148,7 @@ private function willReplace(?iterable $values = null): bool
         }
 
         // No shortcuts are applicable if the pipeline was initialized.
-        if ([] !== $this->pipeline && null !== $this->pipeline) {
+        if (!$this->empty()) {
             return false;
         }
 
@@ -230,15 +235,13 @@ public function unpack(?callable $func = null): self
      */
     public function chunk(int $length, bool $preserve_keys = false): self
     {
-        if (null === $this->pipeline) {
-            // No-op: null.
+        // No-op: an empty array or null.
+        if ($this->empty()) {
             return $this;
         }
 
-        if ([] === $this->pipeline) {
-            // No-op: an empty array.
-            return $this;
-        }
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
 
         // Array shortcut
         if (is_array($this->pipeline)) {
@@ -385,13 +388,8 @@ private static function applyOnce(iterable $previous, callable $func): iterable
      */
     public function filter(?callable $func = null): self
     {
-        if (null === $this->pipeline) {
-            // No-op: null.
-            return $this;
-        }
-
-        if ([] === $this->pipeline) {
-            // No-op: an empty array.
+        // No-op: an empty array or null.
+        if ($this->empty()) {
             return $this;
         }
 
@@ -504,13 +502,8 @@ public function getIterator(): Traversable
      */
     public function toArray(bool $preserve_keys = false): array
     {
-        if (null === $this->pipeline) {
-            // With non-primed pipeline just return an empty array.
-            return [];
-        }
-
-        if ([] === $this->pipeline) {
-            // Empty array is empty.
+        // No-op: an empty array or null.
+        if ($this->empty()) {
             return [];
         }
 
@@ -537,15 +530,13 @@ public function toArray(bool $preserve_keys = false): array
      */
     public function count(): int
     {
-        if (null === $this->pipeline) {
+        if ($this->empty()) {
             // With non-primed pipeline just return zero.
             return 0;
         }
 
-        if ([] === $this->pipeline) {
-            // Empty array is empty.
-            return 0;
-        }
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
 
         $result = 0;
 
@@ -582,11 +573,14 @@ private static function generatorFromIterable(iterable $input): Generator
      */
     public function slice(int $offset, ?int $length = null)
     {
-        if (null === $this->pipeline) {
+        if ($this->empty()) {
             // With non-primed pipeline just move along.
             return $this;
         }
 
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
+
         if (0 === $length) {
             // We're not consuming anything assuming total laziness.
             $this->pipeline = null;
@@ -773,11 +767,17 @@ private static function toIterators(iterable ...$inputs): array
      */
     public function reservoir(int $size, ?callable $weightFunc = null): array
     {
-        if (null === $this->pipeline) {
+        if ($this->empty()) {
             return [];
         }
 
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
+
         if ($size <= 0) {
+            // Discard the state to emulate a full consumption
+            $this->pipeline = null;
+
             return [];
         }
 
@@ -886,13 +886,12 @@ private static function random(): float
      */
     public function min()
     {
-        if (null === $this->pipeline) {
+        if ($this->empty()) {
             return null;
         }
 
-        if ([] === $this->pipeline) {
-            return null;
-        }
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
 
         if (is_array($this->pipeline)) {
             /** @psalm-suppress ArgumentTypeCoercion */
@@ -928,13 +927,12 @@ public function min()
      */
     public function max()
     {
-        if (null === $this->pipeline) {
+        if ($this->empty()) {
             return null;
         }
 
-        if ([] === $this->pipeline) {
-            return null;
-        }
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
 
         if (is_array($this->pipeline)) {
             /** @psalm-suppress ArgumentTypeCoercion */
@@ -960,15 +958,13 @@ public function max()
      */
     public function flip()
     {
-        if (null === $this->pipeline) {
+        if ($this->empty()) {
             // No-op: null.
             return $this;
         }
 
-        if ([] === $this->pipeline) {
-            // No-op: an empty array.
-            return $this;
-        }
+        // Static analyzer hint
+        assert(null !== $this->pipeline && [] !== $this->pipeline);
 
         if (is_array($this->pipeline)) {
             $this->pipeline = array_flip($this->pipeline);

From a9fd9114b835a8b3d2202a22ab46538a9babb9b7 Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.com>
Date: Sat, 15 Apr 2023 13:31:14 +0900
Subject: [PATCH 2/6] Tweak infection.json.dist

---
 infection.json.dist | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/infection.json.dist b/infection.json.dist
index ac52786..092ac57 100644
--- a/infection.json.dist
+++ b/infection.json.dist
@@ -1,11 +1,14 @@
 {
-    "timeout": 2,
+    "timeout": 5,
     "source": {
         "directories": [
             "src"
         ]
     },
     "mutators": {
+        "global-ignoreSourceCodeByRegex": [
+            "assert.*"
+        ],
         "@default": true,
         "IdenticalEqual": false,
         "NotIdenticalNotEqual": false

From c15f70366b46295d1800958f2086fea55bcf3ed4 Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.com>
Date: Sat, 15 Apr 2023 13:36:10 +0900
Subject: [PATCH 3/6] Update src/Standard.php

---
 src/Standard.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Standard.php b/src/Standard.php
index beb1b1a..bb03dd9 100644
--- a/src/Standard.php
+++ b/src/Standard.php
@@ -775,7 +775,7 @@ public function reservoir(int $size, ?callable $weightFunc = null): array
         assert(null !== $this->pipeline && [] !== $this->pipeline);
 
         if ($size <= 0) {
-            // Discard the state to emulate a full consumption
+            // Discard the state to emulate full consumption
             $this->pipeline = null;
 
             return [];

From e6fa097e2f8702d68d36295e20d6eff0ba3f0521 Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.com>
Date: Sat, 15 Apr 2023 14:42:18 +0900
Subject: [PATCH 4/6] Use uninitialized state

---
 src/Standard.php | 69 ++++++++++++++++++++++++++++--------------------
 1 file changed, 41 insertions(+), 28 deletions(-)

diff --git a/src/Standard.php b/src/Standard.php
index bb03dd9..a516aeb 100644
--- a/src/Standard.php
+++ b/src/Standard.php
@@ -55,17 +55,30 @@
 class Standard implements IteratorAggregate, Countable
 {
     /**
-     * Pre-primed pipeline. This is not a full `iterable` per se because we exclude IteratorAggregate before assigning a value.
+     * Pre-primed pipeline.
      *
-     * @var ?iterable
+     * This is not a full `iterable` per se because we exclude IteratorAggregate before assigning a value.
      */
-    private ?iterable $pipeline;
+    private iterable $pipeline;
 
     /**
      * Contructor with an optional source of data.
      */
     public function __construct(?iterable $input = null)
     {
+        if (null !== $input) {
+            $this->replace($input);
+        }
+    }
+
+    private function replace(iterable $input): void
+    {
+        if (is_array($input)) {
+            $this->pipeline = $input;
+
+            return;
+        }
+
         // IteratorAggregate is a nuance best we avoid dealing with.
         // For example, CallbackFilterIterator needs a plain Iterator.
         while ($input instanceof IteratorAggregate) {
@@ -77,7 +90,12 @@ public function __construct(?iterable $input = null)
 
     private function empty(): bool
     {
-        return [] === $this->pipeline || null === $this->pipeline;
+        return !isset($this->pipeline) || [] === $this->pipeline;
+    }
+
+    private function discard(): void
+    {
+        $this->pipeline = null;
     }
 
     /**
@@ -91,7 +109,6 @@ public function append(?iterable $values = null): self
         }
 
         // Static analyzer hints
-        assert(null !== $this->pipeline);
         assert(null !== $values);
 
         return $this->join($this->pipeline, $values);
@@ -118,7 +135,6 @@ public function prepend(?iterable $values = null): self
         }
 
         // Static analyzer hints
-        assert(null !== $this->pipeline);
         assert(null !== $values);
 
         return $this->join($values, $this->pipeline);
@@ -152,15 +168,8 @@ private function willReplace(?iterable $values = null): bool
             return false;
         }
 
-        // Install an array as it is.
-        if (is_array($values)) {
-            $this->pipeline = $values;
-
-            return true;
-        }
-
-        // Else we use ownself to handle edge cases.
-        $this->pipeline = new self($values);
+        // Handle edge cases
+        $this->replace($values);
 
         return true;
     }
@@ -285,7 +294,7 @@ public function map(?callable $func = null): self
         }
 
         // That's the standard case for any next stages.
-        if (is_iterable($this->pipeline)) {
+        if (isset($this->pipeline) && is_iterable($this->pipeline)) {
             $this->pipeline = self::apply($this->pipeline, $func);
 
             return $this;
@@ -348,13 +357,13 @@ public function cast(?callable $func = null): self
         }
 
         // We got an array, that's what we need. Moving along.
-        if (is_array($this->pipeline)) {
+        if (is_array($this->pipeline ?? null)) {
             $this->pipeline = array_map($func, $this->pipeline);
 
             return $this;
         }
 
-        if (is_iterable($this->pipeline)) {
+        if (is_iterable($this->pipeline ?? null)) {
             $this->pipeline = self::applyOnce($this->pipeline, $func);
 
             return $this;
@@ -404,7 +413,7 @@ public function filter(?callable $func = null): self
 
         assert($this->pipeline instanceof Iterator);
 
-        /** @psalm-suppress ArgumentTypeCoercion */
+        /** @psalm-suppress1 ArgumentTypeCoercion */
         $this->pipeline = new CallbackFilterIterator($this->pipeline, $func);
 
         return $this;
@@ -455,13 +464,17 @@ public function reduce(?callable $func = null, $initial = null)
      */
     public function fold($initial, ?callable $func = null)
     {
+        if ($this->empty()) {
+            return $initial;
+        }
+
         $func = self::resolveReducer($func);
 
         if (is_array($this->pipeline)) {
             return array_reduce($this->pipeline, $func, $initial);
         }
 
-        foreach ($this as $value) {
+        foreach ($this->pipeline as $value) {
             $initial = $func($initial, $value);
         }
 
@@ -486,15 +499,15 @@ private static function resolveReducer(?callable $func): callable
 
     public function getIterator(): Traversable
     {
-        if ($this->pipeline instanceof Traversable) {
-            return $this->pipeline;
+        if (!isset($this->pipeline)) {
+            return new EmptyIterator();
         }
 
-        if (null !== $this->pipeline) {
-            return new ArrayIterator($this->pipeline);
+        if ($this->pipeline instanceof Traversable) {
+            return $this->pipeline;
         }
 
-        return new EmptyIterator();
+        return new ArrayIterator($this->pipeline);
     }
 
     /**
@@ -583,7 +596,7 @@ public function slice(int $offset, ?int $length = null)
 
         if (0 === $length) {
             // We're not consuming anything assuming total laziness.
-            $this->pipeline = null;
+            $this->discard();
 
             return $this;
         }
@@ -705,7 +718,7 @@ private static function head(iterable $input, int $length): Generator
      */
     public function zip(iterable ...$inputs)
     {
-        if (null === $this->pipeline) {
+        if (!isset($this->pipeline)) {
             $this->pipeline = array_shift($inputs);
         }
 
@@ -776,7 +789,7 @@ public function reservoir(int $size, ?callable $weightFunc = null): array
 
         if ($size <= 0) {
             // Discard the state to emulate full consumption
-            $this->pipeline = null;
+            $this->discard();
 
             return [];
         }

From c35fd1a3f6f4d6d6d26cbbac88927a0e258fbcf3 Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.com>
Date: Sat, 15 Apr 2023 15:01:14 +0900
Subject: [PATCH 5/6] Fix things

---
 .php-cs-fixer.dist.php |  1 +
 psalm.xml.dist         |  3 +++
 src/Standard.php       | 48 ++++++++++++++++++------------------------
 tests/ZipTest.php      |  7 ++++++
 4 files changed, 31 insertions(+), 28 deletions(-)

diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
index f4319d3..971f5e0 100644
--- a/.php-cs-fixer.dist.php
+++ b/.php-cs-fixer.dist.php
@@ -60,6 +60,7 @@
         'random_api_migration' => false,
         'blank_line_between_import_groups' => false,
         'blank_line_before_statement' => ['statements' => ['break', 'continue', 'declare', 'return', 'throw', 'try']],
+        'no_unset_on_property' => false,
     ])
     ->setFinder(
         PhpCsFixer\Finder::create()
diff --git a/psalm.xml.dist b/psalm.xml.dist
index ba31bda..69b36b4 100644
--- a/psalm.xml.dist
+++ b/psalm.xml.dist
@@ -22,5 +22,8 @@
         </ForbiddenCode>
         <MissingClosureParamType errorLevel="suppress" />
         <MissingClosureReturnType errorLevel="suppress" />
+
+        <RedundantPropertyInitializationCheck errorLevel="suppress" />
+        <PropertyNotSetInConstructor errorLevel="suppress" />
     </issueHandlers>
 </psalm>
diff --git a/src/Standard.php b/src/Standard.php
index a516aeb..78ff50a 100644
--- a/src/Standard.php
+++ b/src/Standard.php
@@ -39,7 +39,6 @@
 use function assert;
 use function count;
 use function is_array;
-use function is_iterable;
 use function is_string;
 use function iterator_to_array;
 use function max;
@@ -88,14 +87,20 @@ private function replace(iterable $input): void
         $this->pipeline = $input;
     }
 
+    /**
+     * @psalm-suppress TypeDoesNotContainType
+     */
     private function empty(): bool
     {
         return !isset($this->pipeline) || [] === $this->pipeline;
     }
 
+    /**
+     * @phan-suppress PhanTypeObjectUnsetDeclaredProperty
+     */
     private function discard(): void
     {
-        $this->pipeline = null;
+        unset($this->pipeline);
     }
 
     /**
@@ -249,9 +254,6 @@ public function chunk(int $length, bool $preserve_keys = false): self
             return $this;
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         // Array shortcut
         if (is_array($this->pipeline)) {
             $this->pipeline = array_chunk($this->pipeline, $length, $preserve_keys);
@@ -294,7 +296,7 @@ public function map(?callable $func = null): self
         }
 
         // That's the standard case for any next stages.
-        if (isset($this->pipeline) && is_iterable($this->pipeline)) {
+        if (isset($this->pipeline)) {
             $this->pipeline = self::apply($this->pipeline, $func);
 
             return $this;
@@ -348,6 +350,8 @@ private static function apply(iterable $previous, callable $func): iterable
      *
      * @param ?callable $func a callback must return a value
      *
+     * @psalm-suppress RedundantCondition
+     *
      * @return $this
      */
     public function cast(?callable $func = null): self
@@ -357,13 +361,13 @@ public function cast(?callable $func = null): self
         }
 
         // We got an array, that's what we need. Moving along.
-        if (is_array($this->pipeline ?? null)) {
+        if (isset($this->pipeline) && is_array($this->pipeline)) {
             $this->pipeline = array_map($func, $this->pipeline);
 
             return $this;
         }
 
-        if (is_iterable($this->pipeline ?? null)) {
+        if (isset($this->pipeline)) {
             $this->pipeline = self::applyOnce($this->pipeline, $func);
 
             return $this;
@@ -413,7 +417,7 @@ public function filter(?callable $func = null): self
 
         assert($this->pipeline instanceof Iterator);
 
-        /** @psalm-suppress1 ArgumentTypeCoercion */
+        /** @psalm-suppress ArgumentTypeCoercion */
         $this->pipeline = new CallbackFilterIterator($this->pipeline, $func);
 
         return $this;
@@ -548,9 +552,6 @@ public function count(): int
             return 0;
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         $result = 0;
 
         foreach ($this->pipeline as $value) {
@@ -591,9 +592,6 @@ public function slice(int $offset, ?int $length = null)
             return $this;
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         if (0 === $length) {
             // We're not consuming anything assuming total laziness.
             $this->discard();
@@ -718,8 +716,14 @@ private static function head(iterable $input, int $length): Generator
      */
     public function zip(iterable ...$inputs)
     {
+        if ([] === $inputs) {
+            return $this;
+        }
+
         if (!isset($this->pipeline)) {
-            $this->pipeline = array_shift($inputs);
+            $input = array_shift($inputs);
+            /** @var iterable $input */
+            $this->pipeline = $input;
         }
 
         if ([] === $inputs) {
@@ -784,9 +788,6 @@ public function reservoir(int $size, ?callable $weightFunc = null): array
             return [];
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         if ($size <= 0) {
             // Discard the state to emulate full consumption
             $this->discard();
@@ -903,9 +904,6 @@ public function min()
             return null;
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         if (is_array($this->pipeline)) {
             /** @psalm-suppress ArgumentTypeCoercion */
             return min($this->pipeline);
@@ -944,9 +942,6 @@ public function max()
             return null;
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         if (is_array($this->pipeline)) {
             /** @psalm-suppress ArgumentTypeCoercion */
             return max($this->pipeline);
@@ -976,9 +971,6 @@ public function flip()
             return $this;
         }
 
-        // Static analyzer hint
-        assert(null !== $this->pipeline && [] !== $this->pipeline);
-
         if (is_array($this->pipeline)) {
             $this->pipeline = array_flip($this->pipeline);
 
diff --git a/tests/ZipTest.php b/tests/ZipTest.php
index 116a256..fe3eda4 100644
--- a/tests/ZipTest.php
+++ b/tests/ZipTest.php
@@ -148,6 +148,13 @@ public function testZipNothing(): void
         $this->assertSame([], $pipeline->zip([])->toArray());
     }
 
+    public function testZipNothingNothing(): void
+    {
+        $pipeline = new Standard();
+
+        $this->assertSame([], $pipeline->zip()->toArray());
+    }
+
     public function testExample(): void
     {
         $iterable = range(5, 7);

From 1b8e8a4507b7b31f6408e9dc6d41c7b366b365b9 Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.com>
Date: Sat, 15 Apr 2023 21:01:08 +0900
Subject: [PATCH 6/6] Tweak comment

---
 src/Standard.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Standard.php b/src/Standard.php
index 78ff50a..703f1cc 100644
--- a/src/Standard.php
+++ b/src/Standard.php
@@ -173,7 +173,7 @@ private function willReplace(?iterable $values = null): bool
             return false;
         }
 
-        // Handle edge cases
+        // Handle edge cases there
         $this->replace($values);
 
         return true;