Modern C# Language Design Interview Path

Interview frame

C# records provide value-oriented equality and concise non-destructive mutation, but a domain value object still needs valid construction, stable invariants, and an intentional equality boundary.

Example

public sealed record Money(decimal Amount, string Currency); compares components, yet it accepts negative values and inconsistent currency casing. A stronger type validates and normalizes in a factory or constructor. If a record contains a mutable list, the record can appear unchanged while the list changes, and equality uses the list reference rather than sequence contents.

Design questions

• Which components define identity?
• Can any component change after construction?
• Is normalization part of the invariant?
• Will the object be used as a dictionary key?

The best interview answer distinguishes language-provided mechanics from domain guarantees.