Differentiate between named parameters and positional parameters in Dart?

Both named and positional parameters are part of optional parameter:

Optional Positional Parameters:

• A parameter wrapped by [ ] is a positional optional parameter.

  	```dart
  	getHttpUrl(String server, String path, [int port=80]) {
  	  // ...
  	}
  	```

• You can specify multiple positional parameters for a function:

  	```dart
  	getHttpUrl(String server, String path, [int port=80, int numRetries=3]) {
  	  // ...
  	}
  	```
  	In the above code, `port` and `numRetries` are optional and have default values of 80 and 3 respectively. You can call `getHttpUrl` with or without the third parameter.  The optional parameters are  _positional_  in that you can't omit  `port`  if you want to specify  `numRetries`.

Optional Named Parameters:

• A parameter wrapped by { } is a named optional parameter.

  	```dart
  	getHttpUrl(String server, String path, {int port = 80}) {
  	  // ...
  	}
  	```

• You can specify multiple named parameters for a function:

  	```dart
  	getHttpUrl(String server, String path, {int port = 80, int numRetries = 3}) {
  	  // ...
  	}
  	```
  	You can call `getHttpUrl` with or without the third parameter. You **must** use the parameter name when calling the function.

• Because named parameters are referenced by name, they can be used in an order different from their declaration.

  	```dart
  	getHttpUrl('example.com', '/index.html', numRetries: 5, port: 8080);
  	getHttpUrl('example.com', '/index.html', numRetries: 5);
  	```