Wrap some objects in using statements (#7560)

* Wrap some objects in using statements

* Switch to using statement.

src/Foundation/NSDecimal.cs

@@ -176,42 +176,50 @@ namespace Foundation {
 			
 		public static implicit operator NSDecimal (int value)
 		{
-			return new NSNumber (value).NSDecimalValue;
+			using var number = new NSNumber (value);
+			return number.NSDecimalValue;
 		}
 
 		public static explicit operator int (NSDecimal value)
 		{
-			return new NSDecimalNumber (value).Int32Value;
+			using var number = new NSDecimalNumber (value);
+			return number.Int32Value;
 		}
 
 		public static implicit operator NSDecimal (float value)
 		{
-			return new NSNumber (value).NSDecimalValue;
+			using var number = new NSNumber (value);
+			return number.NSDecimalValue;
 		}
 
 		public static explicit operator float (NSDecimal value)
 		{
-			return new NSDecimalNumber (value).FloatValue;
+			using var number = new NSDecimalNumber (value);
+			return number.FloatValue;
 		}
 
 		public static implicit operator NSDecimal (double value)
 		{
-			return new NSNumber (value).NSDecimalValue;
+			using var number = new NSNumber (value);
+			return number.NSDecimalValue;
 		}
 
 		public static explicit operator double (NSDecimal value)
 		{
-			return new NSDecimalNumber (value).DoubleValue;
+			using var number = new NSDecimalNumber (value);
+			return number.DoubleValue;
 		}
 
 		public static implicit operator NSDecimal (decimal value)
 		{
-			return new NSDecimalNumber (value.ToString (CultureInfo.InvariantCulture)).NSDecimalValue;
+			using var number = new NSDecimalNumber (value.ToString (CultureInfo.InvariantCulture));
+			return number.NSDecimalValue;
 		}
 
 		public static explicit operator decimal (NSDecimal value)
 		{
-			return Decimal.Parse (new NSDecimalNumber (value).ToString (), CultureInfo.InvariantCulture);
+			using var number = new NSDecimalNumber (value);
+			return Decimal.Parse (number.ToString (), CultureInfo.InvariantCulture);
 		}
 
 		public bool Equals (NSDecimal other)
@@ -221,10 +229,7 @@ namespace Foundation {
 
 		public override bool Equals (object obj)
 		{
-			if (!(obj is NSDecimal))
-				return false;
-			
-			return this == (NSDecimal) obj;
+			return obj is NSDecimal other && this == other;
 		}
 		
 		public override int GetHashCode ()

src/Foundation/NSFileManager.cs

@@ -486,7 +486,8 @@ namespace Foundation {
 
 		public NSUrl[] GetMountedVolumes (NSString [] properties, NSVolumeEnumerationOptions options)
 		{
-			return GetMountedVolumes (NSArray.FromNSObjects (properties), options);
+			using var array = NSArray.FromNSObjects (properties);
+			return GetMountedVolumes (array, options);
 		}
 
 		public string CurrentDirectory {

src/Security/Items.cs

@@ -147,7 +147,7 @@ namespace Security {
 					if (max == 1)
 						return new NSData [] { new NSData (ptr, false) };
 
-					var array = new NSArray (ptr);
+					using var array = new NSArray (ptr);
 					var records = new NSData [array.Count];
 					for (uint i = 0; i < records.Length; i++)
 						records [i] = new NSData (array.ValueAt (i), false);
@@ -200,7 +200,7 @@ namespace Security {
 				result = SecItem.SecItemCopyMatching (copy.Handle, out ptr);
 				n = null;
 				if (result == SecStatusCode.Success){
-					var array = new NSArray (ptr);
+					using var array = new NSArray (ptr);
 					var records = new SecRecord [array.Count];
 					for (uint i = 0; i < records.Length; i++)
 						records [i] = new SecRecord (new NSMutableDictionary (array.ValueAt (i), false));