In .NET we’ve got this cool little language construct called default, that’ll give you the default value for any given type. That is, null, for any reference type, or zero/false/DateTime.Min/etc. for value types.

Here it is in action (nothing amazing going on here):

var x =default(DateTime);

So what if you don’t know the type you want the default of at compile time? You can’t say

var y =default(today.GetType());

nor

var z =typeof(DateTime).GetDefault();

That last one would be nice, but that “GetDefault” method doesn’t exist.

I’ve seen several solutions to this, that are basically variations on this theme:

publicstaticobject GetDefaultValue(Type type)
{
    return type.IsValueType
        ?Activator.CreateInstance(type)
: null;
}

This certainly works, but I somehow feel like it’s not exactly perfect since it doesn’t use the *default *operator.

Here is how I normally do it. It sidesteps the IsValueType, and Activator stuff, and uses the built-in default language construct… First it grabs a handle to the GetDefaultGeneric method, and then makes the generic version of it with the specific type. Then it calls it, returning the value.

publicstaticobject GetDefault(thisType type)
{
    var getDefault =typeof(ExtReflection)
                         .GetMethod("GetDefaultGeneric");
    var typed = getDefault.MakeGenericMethod(type);
    
    return typed.Invoke(null, newobject[] { });
}
publicstatic T GetDefaultGeneric<T>()
{
  returndefault(T);
}

Pretty simple, but something I’ve found useful every now and again. I’d guess this technique could be useful in other situations/contexts as well.

Default Value

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