Classes, structs, and interfaces

Classes and structs group data with the operations that work on it. Use a class when identity, shared mutable state, inheritance, or a resource lifecycle is part of the model. Use a struct for a compact value with copy semantics.

class Counter(private var count: int = 0) {
    val Count: int => count

    func Increment() {
        count = count + 1
    }
}

struct Point(val X: double, val Y: double)

An interface describes behavior that several otherwise unrelated types can provide:

interface IPrintable {
    func Print()
}

class Report : IPrintable {
    func Print() {
        Console.WriteLine("Report")
    }
}

Classes, structs, and interfaces can contain methods, properties, indexers, events, nested types, and other members appropriate to their kind. They support generic parameters and constraints, access control, and partial declarations.

Type declarations at namespace scope default to internal; use public to export them from an assembly. Members declared inside a type default to public, although their effective visibility can never exceed that of the containing type.

Learn about types and members

Type declarations and initialization covers primary constructors, fields, generic types, initializers, records, static classes, and ref structs.
Properties and events covers stored and computed properties, accessors, indexers, backing fields, and events.
Inheritance and partial types covers base types, open and sealed hierarchies, overrides, and declarations spread across several source files.
Parameters, overloading, and operators covers parameter behavior, method selection, custom operators, and callable objects.
Interfaces covers interface inheritance and implementation.

Table of Contents

Classes, structs, and interfaces

Learn about types and members