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Named parameters are function parameters identified by their label during invocation rather than their ordinal position. Defined by enclosing the parameter list in curly braces {}, named parameters are optional by default unless explicitly annotated with the required modifier.

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Declaration Syntax

To define named parameters, wrap the specific parameters within curly braces in the function signature. 
void updateSettings({bool? isVisible, int? timeout}) {
  // Function body
}

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Invocation Syntax

When calling a function with named parameters, you must specify the parameter name followed by a colon (:) and the value. The order of arguments does not matter. 
// Valid calls
updateSettings(isVisible: true, timeout: 500);
updateSettings(timeout: 500, isVisible: true);
updateSettings(isVisible: false); // 'timeout' remains null

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Null Safety and Default Values

Because named parameters are optional by default, the Dart analyzer enforces null safety rules to prevent runtime errors. There are three states a named parameter can exist in:
  1. Nullable: The type is explicitly marked with ?, allowing the value to be null if the caller omits the argument.
  2. Default Value: A default value is provided using =, used if the caller omits the argument.
  3. Required: The parameter is annotated with required, mandating that the caller provide a value.
void configure({
  String? label,            // Nullable: defaults to null if omitted
  int retries = 3,          // Default value: defaults to 3 if omitted
  required String host,     // Required: Compiler error if omitted
}) { 
  print('$host, $label, $retries');
}

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Mixing Positional and Named Parameters

A function can accept both positional and named parameters. However, all positional parameters must be declared before the named parameters. 
// 'id' is positional; 'force' and 'verbose' are named
void deleteItem(int id, {bool force = false, bool? verbose}) {
  // ...
}

void main() {
  deleteItem(101, force: true);
}
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