As a developer, “calling” or “executing” functions is the thing you do many times per your working day. It’s a common action. However, in this post, we will try an uncommon way to execute functions in Dart using static Function.apply() method.
1. Syntax
// Syntax
dynamic apply (
Function function,
List? positionalArguments,
[Map<Symbol, dynamic>? namedArguments]
)
// Simple Example
void helloEcomobi() {
print('Hello Ecomobi.');
}
void main() {
Function.apply(helloEcomobi, [], {});
}
// Output
Hello Ecomobi.- function: The name of the function you want to execute (“helloEcomobi”).
- positionalArguments: List of (both required and optional) positional arguments , wrapped in square brackets. In above example, there is no positional argument, therefore we provide empty list ([ ]).
- namedArguments: Map of (optional) named arguments, wrapped in curly brackets. In above example, there is no named argument, therefore we provide empty map ({ }).
- The return type of Function.apply() is the return type of the executed function. In above example, the return type is void.
2. Examples
2a. Execute function with optional named parameters
// Optional named parameters
void helloEcomobi1(int year, {String country, String city}) {
print('Hello Ecomobi. $country, $city $year.');
}
void main() {
Function.apply(helloEcomobi1, [2023], {#country: 'Vietnam', #city: 'Hanoi'});
}
// Output
Hello Ecomobi. Vietnam, Hanoi 2023.- Function helloEcomobi1 has one required positional parameter (year) and two optional named parameters. The “year” is in square brackets, country and city are in curly brackets.
- Each optional named argument starts with a hash character (#)
2b. Execute function with optional positional parameters
// Optional positional parameters
void helloEcomobi2(int year, [String country, String city]) {
print('Hello Ecomobi. $country, $city $year.');
}
void main() {
Function.apply(helloEcomobi2, [2023, 'Vietnam', 'Hanoi']);
}
// Output
Hello Ecomobi. Vietnam, Hanoi 2023.- All positional parameters (both required and optional) are in the square brackets.
2c. Execute function with return value
// With return value
int sum(int a, int b) {
return a + b;
}
void main() {
int result = Function.apply(sum, [1, 2]);
print('Sum = $result');
}
// Output
Sum = 3
