In dart Default Optional Parameter means that if we do not need to print null value than we can define the value in function , so whenever we do not call the value in main function than by default pre-define value will be print which we have define in function at the time of creation. this method we can use in Named parameter and Optional parameter.
And . if we define the value in main function than the function call the value which is define in the main function and ignore the default value which is ser by default.
I have already write both example to learn easily.
//Named Parameter
void student(var name ,{ var roll })
{
print("Name = $name");
print("Roll No = $roll");
}
// Optional Parameter
void student1(var name ,[ var roll ])
{
print("Name = $name");
print("Roll No = $roll");
}
void main() {
student("Vinit");
student1("Jay");
}
Name = Vinit
Roll No = null
Name = Jay
Roll No = null
In above example we can see that we use both name and optional parameter and we did not pass any value of this in main function , hence we can see output as null.
In below example we use by default value.
```dart //Named Parameter void student(var name ,{ var roll = 2 })
{ print("Name = $name"); print("Roll No = $roll");
}
// Optional Parameter void student1(var name ,[ var roll = 2 ])
{ print("Name = $name"); print("Roll No = $roll");
}
void main() { student("Vinit"); student1("Jay");
}
Name = Vinit Roll No = 1 Name = Jay Roll No = 2 ```