[10.x] Add charAt method to both Str and Stringable (#46349)

* [10.x] Add charAt method to both Str and Stringable

* Update Str.php

* Update Stringable.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/Illuminate/Support/Str.php

@@ -216,6 +216,24 @@ public static function camel($value)
         return static::$camelCache[$value] = lcfirst(static::studly($value));
     }
 
+    /**
+     * Get the character at the specified index.
+     *
+     * @param  string  $subject
+     * @param  int  $index
+     * @return string|null
+     */
+    public static function charAt($subject, $index)
+    {
+        $length = mb_strlen($subject);
+
+        if ($index < 0 ? $index < -$length : $index > $length - 1) {
+            return null;
+        }
+
+        return mb_substr($subject, $index, 1);
+    }
+
     /**
      * Determine if a given string contains a given substring.
      *

src/Illuminate/Support/Stringable.php

@@ -99,6 +99,17 @@ public function basename($suffix = '')
         return new static(basename($this->value, $suffix));
     }
 
+    /**
+     * Get the character at the specified index.
+     *
+     * @param  int  $index
+     * @return string|null
+     */
+    public function charAt($index)
+    {
+        return Str::charAt($this->value, $index); 
+    }
+
     /**
      * Get the basename of the class path.
      *

tests/Support/SupportStrTest.php

@@ -749,6 +749,16 @@ public function testCamel()
         $this->assertSame('fooBarBaz', Str::camel('foo-bar_baz'));
     }
 
+    public function testCharAt()
+    {
+        $this->assertEquals('р', Str::charAt('Привет, мир!', 1));
+        $this->assertEquals('ち', Str::charAt('「こんにちは世界」', 4));
+        $this->assertEquals('w', Str::charAt('Привет, world!', 8));
+        $this->assertEquals('界', Str::charAt('「こんにちは世界」', -2));
+        $this->assertEquals(null, Str::charAt('「こんにちは世界」', -200));
+        $this->assertEquals(null, Str::charAt('Привет, мир!', 100));
+    }
+
     public function testSubstr()
     {
         $this->assertSame('Ё', Str::substr('БГДЖИЛЁ', -1));

tests/Support/SupportStringableTest.php

@@ -936,6 +936,16 @@ public function testCamel()
         $this->assertSame('fooBarBaz', (string) $this->stringable('foo-bar_baz')->camel());
     }
 
+    public function testCharAt()
+    {
+        $this->assertEquals('р', $this->stringable('Привет, мир!')->charAt(1));
+        $this->assertEquals('ち', $this->stringable('「こんにちは世界」')->charAt(4));
+        $this->assertEquals('w', $this->stringable('Привет, world!')->charAt(8));
+        $this->assertEquals('界', $this->stringable('「こんにちは世界」')->charAt(-2));
+        $this->assertEquals(null, $this->stringable('「こんにちは世界」')->charAt(-200));
+        $this->assertEquals(null, $this->stringable('Привет, мир!')->charAt('Привет, мир!', 100));
+    }
+
     public function testSubstr()
     {
         $this->assertSame('Ё', (string) $this->stringable('БГДЖИЛЁ')->substr(-1));