Dynamically getting default of a parameter type

Question

Question

I am trying to dynamically get the default for a type that is specified in a ParameterInfo. _methods[methodName] returns a MethodInfo object.

Unfortunately, the compiler doesn't like the "paramType" bit inside the default(paramType). I'm stumped.

Error

The type or namespace name 'paramType' could not be found (are you missing a using directive or an assembly reference?)

C:\Applications\...\MessageReceiver.cs Line 113

Example

object blankObject = null;
foreach (var paramInfo in _methods[methodName].Key.GetParameters())
{
    if (paramInfo.Name == paramName)
    {
        Type paramType = paramInfo.ParameterType;
        blankObject = (object)default(paramType);
    }
}
parameters[i] = blankObject;

score 28 · Accepted Answer · answered Jan 23 '09 at 22:26

28

It's quite simple to implement:

public object GetDefault(Type type)
{
    return type.IsValueType ? Activator.CreateInstance(type) : null;
}

answered Jan 23 '09 at 22:26

Jon Skeet

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Thanks man. It's great to have a celebrity answer my question. :) Repped. – Chris Benard Jan 23 '09 at 22:29
6

Don't get too starstruck. He answers _everyone's_ questions! :) – Michael Meadows Jan 23 '09 at 22:30
@Jon still valid 13 years later or there's something better nowadays? – MatteoSp Oct 21 '22 at 13:59
@MatteoSp: I'd use an expression-bodied member now, but I don't know of a better way of achieving the goal :) – Jon Skeet Oct 21 '22 at 14:02

score 1 · Answer 2 · edited May 23 '17 at 12:00

1

I think default only works with the an actual type. It's a complier shortcut not an actual method. It works well with generics. for example:

public void MyMethod<T>(T obj)
{
   T myvar = default(T);
}

Check out this question I posted a while back:

Default Value for Generics

edited May 23 '17 at 12:00

Community

1
1

answered Jan 23 '09 at 22:22

Micah

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1

Right... I've used it with generics a lot, but now I need to get it from a ParameterInfo. Surely there is a way to do this through reflection or something. – Chris Benard Jan 23 '09 at 22:24

Dynamically getting default of a parameter type

Question

Error

Example

2 Answers2