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Anonymous extension method that allow create a new instance of anonymous with new values, similar to with expression of records in C# and F#
public static class AnonymousExtension
{
static void Main(string[] args)
{
var person = new { FirstName = "Scott", LastName = "Hunter", Sex = 'M', Age = 25 };
var otherPerson = person.With(new { LastName = "Hanselman" });
Console.WriteLine(otherPerson);
}
public static T With<T, U>(this T x, U y)
{
return AnonymousHelper<T, U>.Create(x, y);
}
private static class AnonymousHelper<T, U>
{
public static readonly Func<T, U, T> Create;
static AnonymousHelper()
{
ParameterExpression x = Expression.Variable(typeof(T), "x");
ParameterExpression y = Expression.Variable(typeof(U), "y");
var ctr = typeof(T).GetConstructors()[0];
var values = ctr.GetParameters()
.Select(p =>
{
var instance = typeof(U).GetProperty(p.Name, p.ParameterType) is null ? x : y;
return Expression.Property(instance, p.Name);
});
var exp = Expression.New(ctr, values);
var lam = Expression.Lambda<Func<T, U, T>>(exp, new[] { x, y });
Create = lam.Compile();
}
}
}
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