How can I call default(T) with a type? [duplicate]

This question already has answers here: Programmatic equivalent of default(Type) (14 answers) Closed 9 years ago.

In c# I can use default(T) to get the default value of a type. I need to get the default type at run time from a System.Type. How can I do this?

E.g. Something along the lines of this (which doesn't work)

var type = typeof(int);
var defaultValue = de开发者_JAVA技巧fault(type);

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For a reference type return null, for a value type, you could try using Activator.CreateInstance or calling the default constructor of the type.

public static object Default(Type type)
{
   if(type.IsValueType)
   {
      return Activator.CreateInstance(type);
   }

   return null;
}

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If you're trying to build an expression tree, use Expression.Default:

Expression expression = Expression.Default(type);

One other way you could do this fairly easily would be:

object defaultValue = Array.CreateInstance(type, 1).GetValue(0);

Ugly, but it'll work :) Note that it's hard to get the default value of a nullable type, as it will always be boxed to a null reference.

As noted in comments, there are some obscure scenarios (void and pointer types) where these aren't equivalent, but they're corner cases :)

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That's pretty easy, you just have 2 cases to consider:

• reference types: the default value is always null

• value types: you can easily create an instance using Activator.CreateInstance

  public static object GetDefaultValue(Type type)
  {
      if (type.IsValueType)
      {
          return Activator.CreateInstance(type);
      }
      else
      {
          return null;
      }
  }
  

You could also consider using FormatterServices.GetUninitializedObject instead of Activator.CreateInstance, it's probably faster.