NanoByte Clone Generator

A Roslyn source generator for deep Clone() methods.

Annotate a partial class with [Cloneable] and the member-by-member copy is generated at compile time. No reflection, no runtime dependency, trim- and AOT-safe.

Usage

Add a reference to the NanoByte.CloneGenerator NuGet package to your project. It is an analyzer, so mark it as a build-time-only dependency:

<PackageReference Include="NanoByte.CloneGenerator" PrivateAssets="All" />

You can then make a class cloneable like this:

using NanoByte.CloneGenerator;

[Cloneable]
public partial class Contact
{
    public required string LastName { get; set; }
    public string? FirstName { get; set; }
    public Address? WorkAddress { get; set; }
    public List<PhoneNumber> PhoneNumbers { get; } = [];
}

which generates:

public virtual Contact Clone()
{
    var from = this;
    var to = new Contact {LastName = from.LastName};
    CloneFromTo(from, to);
    return to;
}

protected static void CloneFromTo(Contact from, Contact to)
{
    to.FirstName = from.FirstName;
    to.WorkAddress = from.WorkAddress?.Clone();
    foreach (var item in from.PhoneNumbers) to.PhoneNumbers.Add(item?.Clone()!);
}

No runtime dependency

The marker attributes are internal to each compilation that uses this package. An assembly granted InternalsVisibleTo access to several such projects will therefore see several CloneableAttribute types.

Where to go next

• Attributes: opting in, and the escape hatches
• What gets copied: the member classification rules
• Inheritance: how the CloneFromTo chain works
• Clone interfaces: ICloneable<T> and System.ICloneable

Limitations

• Classes only. Value types are not supported.
• No nested types.
• No cycle detection. An object graph containing a cycle will recurse until the stack runs out.
• Back-references are deep-copied like anything else, which detaches them from the new graph. Use [ShallowClone] where you need identity preserved.