Invoking nested functions in the Dart programming language - dart

Question

I defined an inner function here:
person(firstName, lastName){
fullName(){ //Is it possible to invoke this function outside the 'person' function?
return firstName + " " + lastName;
}
firstInitial(){
return firstName[0];
}
lastInitial(){
return lastName[0];
}
}
Next, I tried to invoke the "fullName" function from the "main" function:
void main() {
print(person("Rob", "Rock").fullName());
}
but it produced this error:
Uncaught TypeError: Cannot read property 'fullName$0' of undefined
Is it possible to invoke an inner function outside the scope where the function is defined?

Answer 1

You can declare the function outside the enclosing block:
void main() {
var fullName;
person(firstName, lastName){
fullName = () => "firstName: $firstName lastName: $lastName";
}
person("Rob", "Rock");
print(fullName());
}
or return it:
void main() {
person(firstName, lastName) => () => "firstName: $firstName"
"lastName: $lastName";
print(person("Rob", "Rock")());
}
If you want this syntax person("Rob", "Rock").fullName() you can return class instance:
class Res{
var _firstName, _lastName;
Res(this._firstName, this._lastName);
fullName() => "firstName: $_firstName lastName: $_lastName";
}
void main() {
person(firstName, lastName) => new Res(firstName,lastName);
print(person("Rob", "Rock").fullName());
}

Answer 2

Those functions can be invoked externally, the issue is that your program can't see them. Your function returns void, so the inner functions are invisible.
But what it looks like you're trying to do is define a class. So a simpler way to do it is
class Person {
var firstName, lastName;
Person(this.firstName, this.lastName);
get fullName => "$firstName $lastName";
firstInitial() => firstName[0];
lastInitial() { return lastName[0]; }
}
main() {
print(new Person("Rob", "Rock).fullName);
print(new Person("Robert", "Stone").lastInitial());
}
For illustration I used three different syntaxes for the three different functions, a getter, a lambda, and a full-blown function.