greendimka

class Program
{
	static void Main(string[] args)
	{
		var config = new MapperConfiguration(c =>
		{
			c.CreateMap<SourceClass, TargetClass>()
				.ForMember(x => x.Vals, o => o.MapFrom((srcCls, trgCls) =>
				{
					trgCls.Vals.Clear();

greendimka

public class Square {
    private int _SideLength;

    public int SideLength {
        get => _SideLength;
        set => _SideLength = value;
    }

    public int Area {
        get => _SideLength * _SideLength;