diff --git a/.php_cs.dist b/.php_cs.dist
index 78bc9fa..c3742ac 100644
--- a/.php_cs.dist
+++ b/.php_cs.dist
@@ -1,4 +1,21 @@
 <?php
+/*
+ * Copyright 2017, 2018 Alexey Kopytko <alexey@kopytko.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
 
 $header = <<<'EOF'
 Copyright 2017, 2018 Alexey Kopytko <alexey@kopytko.com>
@@ -20,6 +37,8 @@ return PhpCsFixer\Config::create()
     ->setRiskyAllowed(true)
     ->setRules([
         '@Symfony' => true,
+        '@Symfony:risky' => true,
+        '@PHP70Migration:risky' => true,
         'array_syntax' => ['syntax' => 'short'],
         'declare_strict_types' => true,
         'explicit_indirect_variable' => true,
@@ -31,13 +50,21 @@ return PhpCsFixer\Config::create()
         'non_printable_character' => true,
         'ordered_imports' => true,
         'php_unit_test_class_requires_covers' => true,
+        'php_unit_strict' => true,
         'phpdoc_add_missing_param_annotation' => true,
         'phpdoc_order' => true,
         'visibility_required' => true,
         'header_comment' => ['header' => $header, 'separate' => 'bottom', 'location' => 'after_open'],
         'ternary_to_null_coalescing' => true,
-        'yoda_style' => null,
+        'yoda_style' => true,
         'phpdoc_to_comment' => false,
+        'strict_comparison' => true,
+        'is_null' => true,
+        'function_to_constant' => true,
+        'void_return' => false,
+        'return_assignment' => true,
+        'array_syntax' => ['syntax' => 'short'],
+        'array_indentation' => true,
     ])
     ->setFinder(
         PhpCsFixer\Finder::create()
diff --git a/Makefile b/Makefile
index 9845e9f..71c9c73 100644
--- a/Makefile
+++ b/Makefile
@@ -40,7 +40,7 @@ COMPOSER=$(PHP) $(shell which composer)
 
 # Infection
 INFECTION=vendor/bin/infection
-MIN_MSI=90
+MIN_MSI=100
 MIN_COVERED_MSI=100
 INFECTION_ARGS=--min-msi=$(MIN_MSI) --min-covered-msi=$(MIN_COVERED_MSI) --threads=$(JOBS) --coverage=build/logs --log-verbosity=default --show-mutations
 
diff --git a/composer.json b/composer.json
index ba5c773..ec22c37 100644
--- a/composer.json
+++ b/composer.json
@@ -27,7 +27,10 @@
         "psr-4": {"Pipeline\\": "src/"}
     },
     "autoload-dev": {
-        "psr-4": {"Pipeline\\": "tests/"}
+        "psr-4": {
+            "Tests\\Pipeline\\": "tests/",
+            "Pipeline\\": "tests/"
+        }
     },
     "require": {
         "php": ">=7"
diff --git a/example.php b/example.php
index db9b850..e6a22a2 100644
--- a/example.php
+++ b/example.php
@@ -29,9 +29,9 @@
 });
 
 // next processing step
-$pipeline->map(function ($i) {
-    yield pow($i, 2);
-    yield pow($i, 3);
+$pipeline->map(function ($value) {
+    yield $value ** 2;
+    yield $value ** 3;
 });
 
 // simple one-to-one mapper
diff --git a/infection.json.dist b/infection.json.dist
index 86f9c88..9c232a3 100644
--- a/infection.json.dist
+++ b/infection.json.dist
@@ -5,6 +5,11 @@
             "src"
         ]
     },
+    "mutators": {
+        "@default": true,
+        "IdenticalEqual": false,
+        "NotIdenticalNotEqual": false
+    },
     "logs": {
         "text": "infection-log.txt",
         "badge": {"branch": "master"}
diff --git a/src/Principal.php b/src/Principal.php
index e6005ff..6ad2693 100644
--- a/src/Principal.php
+++ b/src/Principal.php
@@ -49,14 +49,14 @@ public function map(callable $func)
         // This also allows inheriting classes to replace the pipeline
         if ($func instanceof self) {
             /** @psalm-suppress MixedAssignment */
-            $this->pipeline = call_user_func($func);
+            $this->pipeline = \call_user_func($func);
 
             return $this;
         }
 
         if (!$this->pipeline) {
             /** @psalm-suppress MixedAssignment */
-            $this->pipeline = call_user_func($func);
+            $this->pipeline = \call_user_func($func);
 
             // Not a generator means we were given a simple value to be treated as an array
             if (!($this->pipeline instanceof \Generator)) {
diff --git a/src/Simple.php b/src/Simple.php
index 16b4767..d1ad0c3 100644
--- a/src/Simple.php
+++ b/src/Simple.php
@@ -22,7 +22,7 @@
 /**
  * Legacy alias from early days. Please do not remove.
  *
- * @deprecated
+ * @deprecated use Standard
  */
 class Simple extends Standard
 {
diff --git a/src/Standard.php b/src/Standard.php
index 391460b..59cd8c5 100644
--- a/src/Standard.php
+++ b/src/Standard.php
@@ -49,7 +49,7 @@ public function unpack(callable $func = null)
     public function filter(callable $func = null)
     {
         // Strings usually are internal functions, which require exact number of parameters.
-        if (is_string($func)) {
+        if (\is_string($func)) {
             $func = static function ($value) use ($func) {
                 return $func($value);
             };
diff --git a/tests/ArraysTest.php b/tests/ArraysTest.php
new file mode 100644
index 0000000..d05ea13
--- /dev/null
+++ b/tests/ArraysTest.php
@@ -0,0 +1,70 @@
+<?php
+/*
+ * Copyright 2017, 2018 Alexey Kopytko <alexey@kopytko.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace Tests\Pipeline;
+
+use PHPUnit\Framework\TestCase;
+use Pipeline\Standard;
+
+/**
+ * @covers \Pipeline\Standard
+ * @covers \Pipeline\Principal
+ */
+class ArraysTest extends TestCase
+{
+    public function testInitialCallbackNotGenerator()
+    {
+        $pipeline = new Standard();
+        $pipeline->map(function () {
+            return PHP_INT_MAX;
+        });
+
+        $this->assertSame([PHP_INT_MAX], iterator_to_array($pipeline));
+    }
+
+    public function testArrayToArray()
+    {
+        $pipeline = new Standard();
+        $pipeline->map(function () {
+            return 42;
+        });
+
+        $this->assertSame([42], $pipeline->toArray());
+    }
+
+    public function testArrayFilter()
+    {
+        $pipeline = new Standard();
+        $pipeline->map(function () {
+            return false;
+        })->filter()->filter();
+
+        $this->assertSame([], $pipeline->toArray());
+    }
+
+    public function testArrayReduce()
+    {
+        $pipeline = new Standard();
+        $pipeline->map(function () {
+            return 3;
+        });
+
+        $this->assertSame(3, $pipeline->reduce());
+    }
+}
diff --git a/tests/EdgeCasesTest.php b/tests/EdgeCasesTest.php
index b8e91aa..18ecc94 100644
--- a/tests/EdgeCasesTest.php
+++ b/tests/EdgeCasesTest.php
@@ -34,7 +34,7 @@ public function testInitialCallbackNotGenerator()
             return PHP_INT_MAX;
         });
 
-        $this->assertEquals([PHP_INT_MAX], iterator_to_array($pipeline));
+        $this->assertSame([PHP_INT_MAX], iterator_to_array($pipeline));
     }
 
     public function testStandardStringFunctions()
@@ -42,7 +42,7 @@ public function testStandardStringFunctions()
         $pipeline = new Standard(new \ArrayIterator([1, 2, 'foo', 'bar']));
         $pipeline->filter('is_int');
 
-        $this->assertEquals([1, 2], iterator_to_array($pipeline));
+        $this->assertSame([1, 2], iterator_to_array($pipeline));
     }
 
     public function testFilterAnyFalseValue()
@@ -70,7 +70,7 @@ public function testMapUnprimed()
             return 1;
         });
 
-        $this->assertEquals([1], $pipeline->toArray());
+        $this->assertSame([1], $pipeline->toArray());
     }
 
     public function testFilterUnprimed()
@@ -78,7 +78,7 @@ public function testFilterUnprimed()
         $pipeline = new Standard();
         $pipeline->filter()->unpack();
 
-        $this->assertEquals([], $pipeline->toArray());
+        $this->assertSame([], $pipeline->toArray());
     }
 
     public function testUnpackUnprimed()
@@ -88,7 +88,7 @@ public function testUnpackUnprimed()
             return 1;
         });
 
-        $this->assertEquals([1], $pipeline->toArray());
+        $this->assertSame([1], $pipeline->toArray());
     }
 
     public function testInitialInvokeReturnsScalar()
@@ -96,7 +96,7 @@ public function testInitialInvokeReturnsScalar()
         $pipeline = new Standard();
         $pipeline->map($this);
 
-        $this->assertEquals([null], iterator_to_array($pipeline));
+        $this->assertSame([null], iterator_to_array($pipeline));
     }
 
     private function firstValueFromIterator(\Iterator $iterator)
@@ -115,11 +115,11 @@ public function testIteratorIterator()
 
         $iterator = new \IteratorIterator($pipeline);
         /* @var $iterator \Iterator */
-        $this->assertEquals(42, $this->firstValueFromIterator($iterator));
+        $this->assertSame(42, $this->firstValueFromIterator($iterator));
 
         $pipeline = new Standard(new \ArrayIterator([42]));
         $iterator = new \IteratorIterator($pipeline);
-        $this->assertEquals(42, $this->firstValueFromIterator($iterator));
+        $this->assertSame(42, $this->firstValueFromIterator($iterator));
     }
 
     public function testIteratorToArrayWithSameKeys()
@@ -135,7 +135,7 @@ public function testIteratorToArrayWithSameKeys()
             yield $i + 2;
         });
 
-        $this->assertEquals([3, 4], iterator_to_array($pipeline));
+        $this->assertSame([3, 4], iterator_to_array($pipeline));
     }
 
     public function testPointlessReplace()
@@ -171,7 +171,7 @@ public function testInvokeMaps()
         $pipeline = new \Pipeline\Standard(new \ArrayIterator(range(1, 5)));
         $pipeline->map($this);
 
-        $this->assertEquals(range(1, 5), iterator_to_array($pipeline));
+        $this->assertSame(range(1, 5), iterator_to_array($pipeline));
     }
 
     public function __invoke($default = null)
diff --git a/tests/ErrorsTest.php b/tests/ErrorsTest.php
index 1ae34ab..d77b523 100644
--- a/tests/ErrorsTest.php
+++ b/tests/ErrorsTest.php
@@ -61,7 +61,7 @@ public function testPipelineInPipelineUsesSelf()
         });
 
         $pipeline->map($pipeline)->filter(function ($i) {
-            return $i % 2 != 0;
+            return 0 !== $i % 2;
         });
 
         $this->expectExceptionMessage('Cannot resume an already running generator');
diff --git a/tests/IterableTest.php b/tests/IterableTest.php
new file mode 100644
index 0000000..729ee2c
--- /dev/null
+++ b/tests/IterableTest.php
@@ -0,0 +1,98 @@
+<?php
+/*
+ * Copyright 2017, 2018 Alexey Kopytko <alexey@kopytko.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace Tests\Pipeline;
+
+use PHPUnit\Framework\TestCase;
+use Pipeline\Standard;
+
+/**
+ * @covers \Pipeline\Standard
+ * @covers \Pipeline\Principal
+ */
+class IterableTest extends TestCase
+{
+    private static $usesIterable;
+
+    public static function setUpBeforeClass()
+    {
+        if (\PHP_VERSION_ID < 70100) {
+            self::$usesIterable = false;
+
+            return;
+        }
+
+        $reflection = new \ReflectionClass(Standard::class);
+        $type = $reflection->getConstructor()->getParameters()[0]->getType();
+        self::$usesIterable = $type->isBuiltin(); // Traversable isn't builtin
+    }
+
+    protected function setUp()
+    {
+        if (!self::$usesIterable) {
+            $this->markTestSkipped('Not testing iterables: not yet supported by the interface');
+        }
+    }
+
+    public function testArrayToArray()
+    {
+        $pipeline = new Standard([1, 2, 3]);
+        $this->assertSame([1, 2, 3], $pipeline->toArray());
+    }
+
+    public function testArrayToIterator()
+    {
+        $pipeline = new Standard([1, 2, 3]);
+        $this->assertSame([1, 2, 3], iterator_to_array($pipeline));
+    }
+
+    public function testEmptyArrayStaysEmpty()
+    {
+        $pipeline = new Standard([]);
+
+        $pipeline->filter()->map(function ($value) {
+            yield $value;
+            yield $value;
+        })->filter()->unpack();
+
+        $this->assertSame([], $pipeline->toArray());
+    }
+
+    public function testArrayFilter()
+    {
+        $pipeline = new Standard([0, 1, 2, 3, 0]);
+        $this->assertSame([1, 2, 3], $pipeline->filter()->toArray());
+    }
+
+    public function testArrayMap()
+    {
+        $pipeline = new Standard([1 => 0, 1, 2, 3]);
+        $this->assertSame([0 => 0, 1, 2, 3], $pipeline->map(function ($value) {
+            return $value;
+        })->toArray());
+    }
+
+    public function testArrayMapFilter()
+    {
+        $pipeline = new Standard([1 => 0, 1, 2, 3]);
+        $this->assertSame([0 => 1, 2, 3], $pipeline->map(function ($value) {
+            return $value;
+        })->filter()->toArray());
+    }
+}
diff --git a/tests/LeaguePipelineTest.php b/tests/LeaguePipelineTest.php
index 0d52939..7afc456 100644
--- a/tests/LeaguePipelineTest.php
+++ b/tests/LeaguePipelineTest.php
@@ -34,11 +34,11 @@ public function testWithLeaguePipeline()
             return $payload * 2;
         });
 
-        $this->assertEquals(22, $leaguePipeline(10));
+        $this->assertSame(22, $leaguePipeline(10));
 
         $pipeline = new \Pipeline\Standard(new \ArrayIterator([10, 20, 30]));
         $pipeline->map($leaguePipeline);
 
-        $this->assertEquals([22, 42, 62], iterator_to_array($pipeline));
+        $this->assertSame([22, 42, 62], iterator_to_array($pipeline));
     }
 }
diff --git a/tests/StandardTest.php b/tests/StandardTest.php
index 7667341..93be442 100644
--- a/tests/StandardTest.php
+++ b/tests/StandardTest.php
@@ -29,10 +29,10 @@ class StandardTest extends TestCase
 {
     public function testEmpty()
     {
-        $this->assertEquals([], iterator_to_array(new Standard()));
+        $this->assertSame([], iterator_to_array(new Standard()));
 
         $pipeline = new Standard();
-        $this->assertEquals([], $pipeline->toArray());
+        $this->assertSame([], $pipeline->toArray());
     }
 
     public function testSingle()
@@ -45,7 +45,7 @@ public function testSingle()
             }
         });
 
-        $this->assertEquals([1, 2, 3], iterator_to_array($pipeline));
+        $this->assertSame([1, 2, 3], iterator_to_array($pipeline));
     }
 
     public function testDouble()
@@ -64,7 +64,7 @@ public function testDouble()
             yield $i * 1000;
         });
 
-        $this->assertEquals([10, 100, 1000, 20, 200, 2000, 30, 300, 3000], $pipeline->toArray());
+        $this->assertSame([10, 100, 1000, 20, 200, 2000, 30, 300, 3000], $pipeline->toArray());
     }
 
     public function testTriple()
@@ -72,8 +72,8 @@ public function testTriple()
         $pipeline = new Standard(new \ArrayIterator(range(1, 3)));
 
         $pipeline->map(function ($i) {
-            yield pow($i, 2);
-            yield pow($i, 3);
+            yield $i ** 2;
+            yield $i ** 3;
         });
 
         $pipeline->map(function ($i) {
@@ -91,7 +91,7 @@ public function testTriple()
             }
         });
 
-        $this->assertEquals([52, 104], $pipeline->toArray());
+        $this->assertSame([52, 104], $pipeline->toArray());
     }
 
     public function testFilter()
@@ -105,7 +105,7 @@ public function testFilter()
         });
 
         $pipeline->filter(function ($i) {
-            return $i % 7 == 0;
+            return 0 === $i % 7;
         });
 
         $pipeline->map(function ($i) {
@@ -114,7 +114,7 @@ public function testFilter()
 
         $pipeline->filter();
 
-        $this->assertEquals([6, 13, 20, 27, 34, 41, 48], $pipeline->toArray());
+        $this->assertSame([6, 13, 20, 27, 34, 41, 48], $pipeline->toArray());
     }
 
     public function testReduce()
@@ -129,7 +129,7 @@ public function testReduce()
 
         $result = $pipeline->reduce();
 
-        $this->assertEquals(55, $result);
+        $this->assertSame(55, $result);
     }
 
     public function testReduceFloat()
@@ -144,7 +144,7 @@ public function testReduceFloat()
 
         $result = $pipeline->reduce();
 
-        $this->assertEquals(55 * 1.05, $result);
+        $this->assertSame(55 * 1.05, $result);
     }
 
     public function testReduceArrays()
@@ -159,7 +159,7 @@ public function testReduceArrays()
 
         $result = $pipeline->reduce(null, []);
 
-        $this->assertEquals([1, 2], $result);
+        $this->assertSame([1, 2], $result);
     }
 
     public function testReduceToArray()
@@ -173,12 +173,12 @@ public function testReduceToArray()
         });
 
         $pipeline->map(function ($i) {
-            yield pow($i, 2);
-            yield pow($i, 3);
+            yield $i ** 2;
+            yield $i ** 3;
         });
 
         $pipeline->filter(function ($i) {
-            return $i % 3 == 0;
+            return 0 === $i % 3;
         });
 
         // just what iterator_to_array does
@@ -188,7 +188,7 @@ public function testReduceToArray()
             return $sum;
         }, []);
 
-        $this->assertEquals([9, 27, 36, 216, 81, 729], $result);
+        $this->assertSame([9, 27, 36, 216, 81, 729], $result);
     }
 
     public function testMeaningless()
@@ -201,7 +201,7 @@ public function testMeaningless()
             yield $i + 1;
         });
 
-        $this->assertEquals(0, $pipeline->reduce());
+        $this->assertSame(0, $pipeline->reduce());
     }
 
     public function testPipelineInPipeline()
@@ -214,10 +214,10 @@ public function testPipelineInPipeline()
 
         $pipeline2 = new Standard();
         $pipeline2->map($pipeline1)->filter(function ($i) {
-            return $i % 2 != 0;
+            return 0 !== $i % 2;
         });
 
-        $this->assertEquals(3 + 5 + 7 + 11, $pipeline2->reduce());
+        $this->assertSame(3 + 5 + 7 + 11, $pipeline2->reduce());
 
         $foo = new Standard();
         $foo->map(function () {
@@ -227,7 +227,7 @@ public function testPipelineInPipeline()
 
         $bar = new Standard();
         $bar->map($foo);
-        $this->assertEquals(3, $bar->reduce());
+        $this->assertSame(3, $bar->reduce());
     }
 
     public function testFiltersPipeline()
@@ -240,10 +240,10 @@ public function testFiltersPipeline()
 
         $output = new Standard($input);
         $output->filter(function ($i) {
-            return $i % 2 != 0;
+            return 0 !== $i % 2;
         });
 
-        $this->assertEquals(3 + 5 + 7 + 11, $output->reduce());
+        $this->assertSame(3 + 5 + 7 + 11, $output->reduce());
     }
 
     private $double;
@@ -255,14 +255,14 @@ public function testTestableGenerator()
             return $value * 2;
         };
 
-        $this->assertSame(8, call_user_func($this->double, 4));
+        $this->assertSame(8, \call_user_func($this->double, 4));
 
         $this->plusone = function ($value) {
             yield $value;
             yield $value + 1;
         };
 
-        $this->assertSame([4, 5], iterator_to_array(call_user_func($this->plusone, 4)));
+        $this->assertSame([4, 5], iterator_to_array(\call_user_func($this->plusone, 4)));
 
         // initial generator
         $sourceData = new \ArrayIterator(range(1, 5));
@@ -286,8 +286,8 @@ public function testMethodChaining()
             yield $b;
             yield $c;
         })->map(function ($i) {
-            yield pow($i, 2);
-            yield pow($i, 3);
+            yield $i ** 2;
+            yield $i ** 3;
         })->map(function ($i) {
             return $i - 1;
         })->map(function ($i) {
@@ -299,6 +299,6 @@ public function testMethodChaining()
             return $i;
         });
 
-        $this->assertEquals([52, 104], iterator_to_array($pipeline));
+        $this->assertSame([52, 104], iterator_to_array($pipeline));
     }
 }
diff --git a/tests/UnpackTest.php b/tests/UnpackTest.php
index 6bfaf07..efd6ec7 100644
--- a/tests/UnpackTest.php
+++ b/tests/UnpackTest.php
@@ -44,7 +44,7 @@ public function testMapVector()
             return sqrt($x ** 2 + $y ** 2);
         });
 
-        $this->assertEquals(37, round($pipeline->reduce()));
+        $this->assertSame(37.0, round($pipeline->reduce()));
     }
 
     /**
@@ -61,7 +61,7 @@ public function testFlatMap()
             yield [7, 8, 9, 10];
         })->unpack();
 
-        $this->assertEquals((10 * 11) / 2, round($pipeline->reduce()));
+        $this->assertSame((10 * 11) / 2, $pipeline->reduce());
     }
 
     /**