I would like to know if it is possible to create an instance of a type known only at runtime and assign values to the properties of this instance by using compiled expressions and if so how it is to be done.
I have a generic class with a method which accepts an instance of T and returns a copy. T is only known at runtime or rather is user/consumer defined. I know how to do so with reflection (assuming it has an empty constructor in this example and without exception handling or null checks for simplification).
public class MyClass<T>
{
public T CreateCopy(T source)
{
var type = typeof(T);
var copy = type.GetConstructor(Type.EmptyTypes).Invoke(null);
foreach(var pi in type.GetProperties())
{
pi.SetValue(copy, pi.GetValue(source));
}
return copy;
}
}
Reflection is quite expensive and after some digging i found an option to at least create an instance of T with compiled expressions.
var type = typeof(T);
Expression.Lambda<Func<T>>(Expression
.New(type.GetConstructor(Type.EmptyTypes)
?? throw new InvalidOperationException(
$"Type has to have an empty public constructor. {type.Name}")))
.Compile();
After some benchmarking i have found out that it performs around 6 times faster than the CreateCopy(...) method. The thing is that i do not know which type will be passed in as a generic and how many properties it will have. Is there a way to do all of the operations from CreateCopy(...) method with compiled expressions?
Ihave looked into Expression.Asign, Expression.MemberInit but i am not able to find anything appropriate. The problem with Expression.MemberInit ist that it expects to have an Expresssion.Bind and Expression.Constant but i cant get the values of the properties from the passed instance of T into it. Is there a way?
Thank you.
P.S. So i am looking for something like:
var type = typeof(T);
var propertyInfos = type.GetProperties();
var ctor = Expression.New(type.GetConstructor(Type.EmptyTypes));
var e = Expression.Lambda<Func<T, T>>(Expression
.MemberInit(ctor, propertyInfos.Select(pi =>
Expression.Bind(pi, Expression.Constant(pi.GetValue(source)))))).Compile();
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