In Dart, we can set default values for function or method arguments. The default value is used in case the argument is not passed during the function call.
Here is an example of a function with one argument and a default value in Dart:
void greet(String name, {String message = 'Hello'}) {
print('$message $name');
}
In the above code, the greet function takes one required argument name of type String and one optional named argument message of type String. The message argument has a default value of 'Hello'.
You can call this function with or without the message argument:
greet('John'); // prints "Hello John"
greet('Mary', message: 'Hi'); // prints "Hi Mary"
In the first example, only the required argument name is passed, so the default value of message ('Hello') is used. In the second example, both name and message are passed and the value of message is assigned to 'Hi', so 'Hi Mary' is printed.
We can also set default values for positional arguments:
void showMessage(String name, [String message = 'Welcome']) {
print('$name, $message');
}
In the above code, the showMessage function takes one required positional argument name, and one optional positional argument message. The message argument has a default value of 'Welcome'.
You can call the function with or without the message argument:
showMessage('John'); // prints "John, Welcome"
showMessage('Mary', 'Thanks for coming'); // prints "Mary, Thanks for coming"
In the first example, only the required argument name is passed, so the default value of message ('Welcome') is used. In the second example, both name and message are passed, and the value of message is assigned to 'Thanks for coming', so 'Mary, Thanks for coming' is printed.