language-csharp

C# / .NET

.NET 8 project shape

• Prefer SDK-style projects with explicit TargetFramework (net8.0) and shared defaults in Directory.Build.props.
• Keep nullable reference types enabled for new code: <Nullable>enable</Nullable>.
• Use ImplicitUsings when the repository already does; avoid hand-maintaining noisy common imports.
• Keep application, domain, infrastructure, and test projects separate when boundaries are real, not just for ceremony.

<PropertyGroup>
  <TargetFramework>net8.0</TargetFramework>
  <Nullable>enable</Nullable>
  <ImplicitUsings>enable</ImplicitUsings>
</PropertyGroup>

Nullable reference types

• Treat warnings as design feedback, not noise. Model absence with T?, required, or a domain type.
• Validate nullable inputs at boundaries; keep internals non-null where possible.
• Use ArgumentNullException.ThrowIfNull(value) for guard clauses.
• Avoid ! except when bridging a framework or serializer limitation; leave a short reason.

public sealed class User
{
    public required string Email { get; init; }
    public string? DisplayName { get; init; }
}

Records and value semantics

• Use record or readonly record struct for immutable value-like data.
• Use classes for identity, lifecycle, mutation, or behavior-heavy objects.
• Be deliberate with with: it is copy-with-change, not validation unless constructors enforce invariants.

public sealed record Money(decimal Amount, string Currency);

var discounted = price with { Amount = price.Amount * 0.9m };

Pattern matching

• Use patterns for shape-based branching, parsing, and closed domain states.
• Prefer switch expressions when every case returns a value.
• Keep guards (when) simple; complex decisions deserve named methods.

return command switch
{
    CreateUser(var email) when email.Contains('@') => Create(email),
    DeleteUser(var id) => Delete(id),
    _ => throw new InvalidOperationException("unsupported command")
};