Summary - Metaprogramming

Combine reflection, mirrors and source_gen to write a code generator.

Summary - Metaprogramming

This group surveyed Dart's metaprogramming tools: dart:mirrors (runtime reflection), runtimeType (basic type info), Function.apply (dynamic invocation), macros (Dart 3, compile time), source_gen (build-step code generation).

Practical choice: source_gen for Flutter/AOT (json_serializable, freezed); dart:mirrors for the Dart VM; macros for the future.

Each tool has a different cost: mirrors are slow at runtime, source_gen costs pre-compile but is free at runtime.

Exercise Summary: square via Function.apply

Define a top-level int square(int x) => x * x; function. Inside main add var r = Function.apply(square, [5]); and print(r);.

Show example solution

int square(int x) => x * x;

void main() {
  var r = Function.apply(square, [5]);
  print(r);
}

Test yourself

Best option for Flutter?
- manual code
- dart:mirrors
- only runtimeType
- source_gen
Show answer

source_gen — source_gen works in Flutter/AOT and has no runtime cost.
Match the tools

dart:mirrors

Runtime reflection
source_gen

Build step
Function.apply

Dynamic call
runtimeType

Type info

Dynamic function call

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

Show answer

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

Next lesson: shelf

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