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Optional Parameters in Dart Programming
Optional parameters are those parameters that don't need to be specified when calling the function. Optional parameters allow us to pass default values to parameters that we define. There are two types of optional parameters, mainly −
Ordered (positional) optional parameters
Named optional parameters
Ordered Optional Parameters
Ordered optional parameters are those parameters that are wrapped in [ ]. For example,
void printSomething(int a, int b, [ int c = 10] ){
// function body
}They give us the freedom to call the function with or without the third parameter.
Example
Consider the example shown below −
void printSomething(int a, int b, [ int c = 99]){
print(a + b + c);
}
void main(){
printSomething(2,3);
printSomething(2,3,5);
}In the above example, we can notice easily that when we invoke the printSomething() function for the first time we are not passing any argument, and the next time we invoke the function we are passing 5 as an argument to the third parameter of the printSomething() function.
Output
104 10
Named Optional Parameters
A parameter wrapped by { } is a named optional parameter. Also, it is necessary for you to use the name of the parameter if you want to pass your argument.
Example
Consider the example shown below −
void printSomething(int a, int b, {int c = 99}){
print(a + b + c);
}
void main(){
printSomething(2,3);
printSomething(2,3,c : 10);
}Notice that when invoking the printSomething function for the second time we wrote the name of the parameter c, followed by a colon and the value that we want to pass an argument.
Output
104 15
We can also have multiple named optional parameters too.
Example
Consider the example shown below −
void printSomething(int a, int b, {int c = 99, int d = 100}){
print(a + b + c + d);
}
void main(){
printSomething(2,3,c : 10);
printSomething(2,3,c : 10 , d : 11);
}Output
115 26
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