All 7 Dart Collections & Generics questions
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What are the three main built in collection types in Dart, List, Set, and Map, and what makes each one uniquely suited for a different kind of data storage need? How do commonly used higher order collection methods, such as map, where, and reduce, let you transform and filter Dart collections in a clean, declarative style? How do you create a custom generic class in Dart, and why would a generic class be preferable to writing several nearly identical, separate classes each hardcoded for a different specific type? What are unmodifiable and immutable collections in Dart, and why might you deliberately choose to use one instead of a regular mutable collection in certain parts of your code? How do bounded type parameters, using the extends keyword within a generic class definition, let you constrain a generic type to only accept types that satisfy a specific requirement? What are the performance and memory tradeoffs between using a List, a LinkedHashMap, and a HashSet in Dart when working with a genuinely very large collection of data?
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What are generics in Dart, and how does declaring a collection like List<String> let the Dart compiler catch type related mistakes before your code even runs?

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Answer

Generics let you parameterize a class or a collection type with a specific type, such as declaring a List specifically intended to hold only String values as List<String>, and this lets the Dart compiler verify at compile time that only values of that exact expected type are ever actually added to that collection, immediately catching an accidental mistake, such as trying to add an integer to a list that was explicitly declared to hold only strings, well before that mistake could ever cause a genuine runtime error somewhere later in your actual running application.
List<String> names = ['Alex', 'Sarah'];
names.add(42); // Compile time error: an int cannot be assigned to a String list
Real-world example A developer accidentally attempts to add a numeric user ID directly into a list explicitly typed as List<String> intended for names, and the Dart compiler immediately catches this specific type mismatch mistake before the app is even run.

Common follow-ups: Can a generic type parameter itself be another generic type, such as a List of Lists?;What is the difference between using dynamic and using a specific generic type parameter?

Dart Null Safety;Dart Language Basics & Syntax
All 7 Dart Collections & Generics questions