Question: I want to specify required default constructrion options for my T:

```
  public interface IParameter<T>  /* where T : T(string) */ { 
     T Value { get; set; }
  }

```

so I would be able to construct it from given string if passible like this:

```
Value  = "bla";

```

or at least like this:

```
Value = new T("bla");

```

So how to specify in C# generics such T that is constructible from string?

Answer: 
Unfortunately, that constraint is not legal. Only the parameterless constructor constraint is allowed:

```
where T : new()

```
You can't specify a constructor in an interface. Depending on your requirements you could use an abstract class:

Pseudo code as not at machine with VS:

```
public abstract class BaseParameter<T>
{ 
    public abstract void BaseParameter(string something);

    T Value { get; set; }
}

```