All 17 Generics questions
More in Generics
What are generics and why use them? What problem do generics solve compared to writing a method or class that accepts 'object'? How do you declare a generic class with a type parameter, and how do you instantiate it with a specific type? What is covariance and contravariance in generics? Why can't you use operators like + directly on an unconstrained generic T? How do generic type constraints ('where T : ...') restrict what types can be used, and what are the common constraint kinds? How does generic type inference work when calling a generic method, and when do you need to specify the type argument explicitly? What is covariance ('out T') and contravariance ('in T') in generic interfaces, and how does IEnumerable<out T> demonstrate covariance? What are generics in C#, and what specific problems do they solve compared to writing type-specific code? How are generics implemented for value types vs reference types in the CLR?
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C# › Generics

What are generic constraints and why are they needed?

Intermediate

Answer

Constraints (where T : ...) restrict the type argument so you can use its members — e.g. class, struct, new(), a base type, or an interface.
T Create<T>() where T : new() => new T();
void Sort<T>(List<T> x) where T : IComparable<T> {}
Real-world example Constraining a repository's entity to a base Entity type so you can read its Id.
All 17 Generics questions