Dynamic invoke

Learn dynamic invoke with reflectable.

Dynamic method invocation

Reflection lets you take a method name (as a Symbol) and invoke it at runtime. In dart:mirrors, instanceMirror.invoke(symbol, args) does this.

An alternative without mirrors: Function.apply(fn, args). It dynamically calls a function with an argument list. Example: Function.apply(add, [3, 4]).

Another route: override noSuchMethod to catch unknown method calls. Combined with the dynamic type, flexible proxy classes can be written.

Function.apply example

Function.apply(fn, positionalArgs, namedArgs) calls fn with the given arguments. positionalArgs is a List, namedArgs a Map<Symbol, dynamic>.

Example: int add(int a, int b) => a + b; var r = Function.apply(add, [3, 4]);. The result is 7, just like add(3, 4).

Usage: selecting a method from a command-line argument, calling with parameter lists in test frameworks.

Exercise Add with Function.apply

Define a top-level int add(int a, int b) => a + b; function. Inside main add var r = Function.apply(add, [3, 4]); and print(r);.

Show example solution

int add(int a, int b) => a + b;

void main() {
  var r = Function.apply(add, [3, 4]);
  print(r);
}

Test yourself

Dynamic invocation routes

Function.apply

Call function
mirror.invoke

Call method
noSuchMethod

Unknown call
dynamic

Drop type checks
What does Function.apply do?
- Calls a function with an argument list
- Renames a method
- Returns a Future
- Creates a class
Show answer

Calls a function with an argument list — Function.apply calls fn with the given arguments.

Call the function

var r = ____(add, [3, 4]);

Show answer

var r = Function.apply(add, [3, 4]);

Next lesson: Macro

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies