允许可选的构造函数参数传递给`T` 方法吗？

Question

I have this method that creates an instance of a class, measures the time it takes to load the class, and has the option to call a method. I'm currently trying to implement the option to pass parameters to the constructor of this method (IE T ) but I'm a bit stuck, can anyone help?

public static T CreateInstanceOf<T>(Action<T> configure = null) where T : new()
{
    var stopwatch = Stopwatch.StartNew();

    var result = new T();

    configure?.Invoke(result);

    stopwatch.Stop();

    Logger.Trace("Loaded " + result.GetType().Name + " [took " + stopwatch.ElapsedMilliseconds + "ms]");

    return result;
}

Answer 1

It's much easier if you keep the work of creating class instances out of this method, since the purpose isn't really to create objects - you just want to time the constructors. You could write your method like this instead:

public T TimeCreationOf<T>(Func<T> creator, Action<T> configure = null)
{
    var stopwatch = Stopwatch.StartNew();

    var result = creator.Invoke();

    configure?.Invoke(result);

    stopwatch.Stop();

    Logger.Trace("Loaded " + result.GetType().Name + " [took " + stopwatch.ElapsedMilliseconds + "ms]");

    return result;
}

(Since you're just timing, do you need this method to return the instance of T that was created?)

Now what you pass into this method is a function that returns a T . And since what you want to time is the constructor, you can just pass in a function that calls the constructor and returns an instance of T .

This makes it much easier because you don't need the new() constraint - T could be any type with any sort of constructor. And you don't need to worry about how the "timing" method will call the constructors - the functions you're passing in do that for you:

TimeCreationOf(() => new ClassOne());
TimeCreationOf(() => new ClassTwo(5, "X"));

Because you're calling the constructors directly you know exactly which constructor you want to call and what to pass to it. If you tried to write a generic method that could create all sorts of objects it would be really difficult.

And if you still need to pass in another Action<T> that performs some additional configuration on the object (and you want to include that in the timing) you can do that as well.

TimeCreationOf(() => new ClassTwo(), c =>
{
    c.SomeProperty = "x";
    c.DoSomethingElse();
});

Answer 2

T is not a method - it's a generic type, that you have required have a parameterless constructor, which you are calling. Since there's not a syntax to specify that the type implement a specific constructor signature, you're left with two options:

1. Use reflection (eg Activator.CreateInstance ) to pass parameters to the constructor and hope that whatever T is at runtime supports those parameters, or

2. Require that T implement some interface that you can use to initialize the object:

    public interface IInitializable { public void Init(...parameters...) } public static T CreateInstanceOf<T>(Action<T> configure = null) where T : new(), IInitializable { T = new T(); T.Initialize(...parameters...); ... }