Added firstKey() and lastKey() methods

README.md

@@ -118,6 +118,7 @@ will return:
 * [filter()](#filter) : Applies a filter to the map elements
 * [find()](#find) : Returns the first matching element
 * [first()](#first) : Returns the first element
+* [firstKey()](#firstkey) : Returns the first key
 * [flip()](#flip) : Exchanges keys with their values
 * [flat()](#flat) : Flattens multi-dimensional elements
 * [from()](#from) : Creates a new map from passed elements
@@ -135,6 +136,7 @@ will return:
 * [krsort()](#krsort) : Reverse sort elements by keys
 * [ksort()](#ksort) : Sort elements by keys
 * [last()](#last) : Returns the last element
+* [lastKey()](#lastkey) : Returns the last key
 * [map()](#map) : Applies a callback to each element and returns the results
 * [merge()](#merge) : Combines elements overwriting existing ones
 * [method()](#method) : Registers a custom method
@@ -806,6 +808,28 @@ The first example will return 'a' and the second one 'x'. The third example
 will throw the exception passed if the map contains no elements.
 
 
+### firstKey()
+
+Returns the first key from the map.
+
+```php
+public function firstKey()
+```
+
+* @return mixed First key of map or `NULL` if empty
+
+**Examples:**
+
+```php
+Map::from( ['a' => 1, 'b' => 2] )->lastKey();
+Map::from( [] )->lastKey();
+```
+
+**Results:**
+
+The first example will return 'a' and the second one `NULL`.
+
+
 ### flat()
 
 Creates a new map with all sub-array elements added recursively
@@ -1312,6 +1336,28 @@ The first example will return 'b' and the second one 'x'. The third example
 will throw the exception passed if the map contains no elements.
 
 
+### lastKey()
+
+Returns the last key from the map.
+
+```php
+public function lastKey()
+```
+
+* @return mixed Last key of map or `NULL` if empty
+
+**Examples:**
+
+```php
+Map::from( ['a' => 1, 'b' => 2] )->lastKey();
+Map::from( [] )->lastKey();
+```
+
+**Results:**
+
+The first example will return 'b' and the second one `NULL`.
+
+
 ### map()
 
 Calls the passed function once for each element and returns a new map for the result.

src/Map.php

@@ -659,8 +659,6 @@ public function find( \Closure $callback, bool $last = false )
 	 * will throw the exception passed if the map contains no elements.
 	 *
 	 * @param mixed $default Default value or exception if the map contains no elements
-	 *
-	 * @param mixed $default Default value if map is empty
 	 * @return mixed First value of map or default value
 	 */
 	public function first( $default = null )
@@ -677,6 +675,29 @@ public function first( $default = null )
 	}
 
 
+	/**
+	 * Returns the first key from the map.
+	 *
+	 * Examples:
+	 *  Map::from( ['a' => 1, 'b' => 2] )->firstKey();
+	 *  Map::from( [] )->firstKey();
+	 *
+	 * Results:
+	 * The first example will return 'a' and the second one NULL.
+	 *
+	 * @return mixed First key of map or NULL if empty
+	 */
+	public function firstKey()
+	{
+		if( function_exists( 'array_key_first' ) ) {
+			return array_key_first( $this->list );
+		}
+
+		reset( $this->list );
+		return key( $this->list);
+	}
+
+
 	/**
 	 * Creates a new map with all sub-array elements added recursively
 	 *
@@ -1147,6 +1168,29 @@ public function last( $default = null )
 	}
 
 
+	/**
+	 * Returns the last key from the map.
+	 *
+	 * Examples:
+	 *  Map::from( ['a' => 1, 'b' => 2] )->lastKey();
+	 *  Map::from( [] )->lastKey();
+	 *
+	 * Results:
+	 * The first example will return 'b' and the second one NULL.
+	 *
+	 * @return mixed Last key of map or NULL if empty
+	 */
+	public function lastKey()
+	{
+		if( function_exists( 'array_key_last' ) ) {
+			return array_key_last( $this->list );
+		}
+
+		end( $this->list );
+		return key( $this->list );
+	}
+
+
 	/**
 	 * Calls the passed function once for each element and returns a new map for the result.
 	 *

tests/MapTest.php

@@ -528,6 +528,18 @@ public function testFirstWithException()
 	}
 
 
+	public function testFirstKey()
+	{
+		$this->assertEquals( 'a', Map::from( ['a' => 1, 'b' => 2] )->firstKey() );
+	}
+
+
+	public function testFirstKeyEmpty()
+	{
+		$this->assertEquals( null, Map::from( [] )->firstKey() );
+	}
+
+
 	public function testFlat()
 	{
 		$m = Map::from( [[0, 1], [2, 3]] );
@@ -828,6 +840,18 @@ public function testLastWithException()
 	}
 
 
+	public function testLastKey()
+	{
+		$this->assertEquals( 'b', Map::from( ['a' => 1, 'b' => 2] )->lastKey() );
+	}
+
+
+	public function testLastKeyEmpty()
+	{
+		$this->assertEquals( null, Map::from( [] )->lastKey() );
+	}
+
+
 	public function testMap()
 	{
 		$m = new Map( ['first' => 'test', 'last' => 'user'] );