Generics vs dynamic
- Dart course
- Intermediate
- Lesson 34/116
- 5 min
Learn the difference between generics and dynamic.
Generics vs dynamic
Generics fix the type at compile time; dynamic leaves the type to runtime. Both give flexibility but the safety level differs.
When you declare List<int>, the compiler knows the list holds only int; list.add('a') is a compile error. When you declare List<dynamic>, any type can be added; the error surfaces only at runtime, when the value is accessed. Generics catch the error early; dynamic is flexible but risky. For maintainable code, generics are preferred.
When to use which?
Generics are the default choice for collections and helper methods; they give type safety and readability. Declarations like List<int> and Map<String, int> surface errors at compile time.
dynamic is for cases where the type is not known up front: external data sources, reflection or temporary prototype code. But in production code dynamic should be a last resort. Generics give a contract to the compiler and the reader; dynamic removes that contract. The right choice is generics, which keeps safety.
Practice Write a generic pick<T> method
Define a generic method named T pick<T>(List<T> items, int i); its body should be return items[i];. In main, call print(pick<int>([1, 2, 3], 1));.
Starter code
// Define the pick<T> method
void main() {
// Call pick<int>([1, 2, 3], 1) and print
}Sample solution
// Define the pick<T> method
T pick<T>(List<T> items, int i) {
return items[i];
}
void main() {
print(pick<int>([1, 2, 3], 1));
}Expected output
2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match generics and dynamic properties
| Term | Meaning |
|---|---|
Generic |
Compile-time safety |
dynamic |
Runtime check |
List<int> |
Fixed type |
2 Build a type-safe list
var ages = <____>[28, 30];
print(ages[0]);var ages = <int>[28, 30];
print(ages[0]);Explanation: <int>[28, 30] produces a type-safe List<int>.
3 Which is the safest choice?
- List<dynamic>
- List<int> Correct answer
- dynamic x
- var x = 5
Explanation: List<int> fixes the type at compile time; it is the safest choice.