Due to the nuances of various
object-oriented programming languages, each has its own methods and
patterns for
implementing and using value objects.
C# In
C#, a
class is a
reference type while a struct (concept derived from the
struct in C language) is a value type. by removing any property setters and only passing member values through the constructors. Example: public record StreetAddress(string Street, string City); or with a more verbose syntax: public class StreetAddress { public StreetAddress(string street, string city) { Street = street; City = city; } public string Street { get; } public string City { get; } }
C++ In C++, a value object can be built by
overloading the
assignment operator and using appropriate
constness constraints on the fields (that will be evaluated once by the
initializer list of the constructor) and on the methods of the class. However, if the fields themselves are declared const (rather than use non-const fields while only exposing "getter" accessors), then it won't be possible to fully overwrite such a value object with another ().
Python Python has data classes which provides equality testing and can be made immutable using the frozen parameter. from dataclasses import dataclass @dataclass(frozen=True) class StreetAddress: """Represents a street address.""" street: str city: str
Java Value objects are available since Java 14, as data records Unlike C# and C++, Java has no support for custom value types at the language level. Every custom type is a reference type, and therefore has identity and reference semantics, though extending support for custom value types is being considered. Java programmers therefore emulate value objects by creating immutable objects, and declaring all attributes to be of immutable type (such as , , or any other type declared in accordance with these rules), not of mutable type such an or even a . They should also define equals and hashCode to compare values rather than references. The term "VALJO" (VALue Java Object) has been coined to refer to the stricter set of rules necessary for a correctly defined immutable value object. StreetAddress = Data.define(:street, :city) ==See also==