Basically I am going through the definition of closure functions which says -
A function that can be referenced with access to the variables in its lexical scope is called a closure
So I want to know this term lexical scope.
lexical scoped variable/closure etc can only be accessed within the block of code in which it is defined.
Dart is a lexically scoped language. With lexical scoping, descendant scopes will access the most recently declared variable of the same name. The innermost scope is searched first, followed by a search outward through other enclosing scopes.
You can “follow the curly braces outwards” to see if a variable is in scope.
See the following example.
main() { //a new scope
String language = "Dart";
void outer() {
//curly bracket opens a child scope with inherited variables
String level = 'one';
String example = "scope";
void inner() { //another child scope with inherited variables
//the next 'level' variable has priority over previous
//named variable in the outer scope with the same named identifier
Map level = {'count': "Two"};
//prints example: scope, level:two
print('example: $example, level: $level');
//inherited from the outermost scope: main
print('What Language: $language');
} //end inner scope
inner();
//prints example: scope, level:one
print('example: $example, level: $level');
} //end outer scope
outer();
} //end main scope
A closure is a function object that has access to variables in its lexical scope, even when the function is used outside of its original scope.
/// Returns a function that adds [addBy] to the
/// function's argument.
Function makeAdder(num addBy) {
return (num i) => addBy + i;
}
void main() {
// Create a function that adds 2.
var add2 = makeAdder(2);
// Create a function that adds 4.
var add4 = makeAdder(4);
assert(add2(3) == 5);
assert(add4(3) == 7);
}
You can read more from here.