C# Language
Nullable types
Effective usage of underlying Nullable argument
Example
Any nullable type is a generic type. And any nullable type is a value type.
There are some tricks which allow to effectively use the result of the Nullable.GetUnderlyingType method when creating code related to reflection/code-generation purposes:
public static class TypesHelper {
public static bool IsNullable(this Type type) {
Type underlyingType;
return IsNullable(type, out underlyingType);
}
public static bool IsNullable(this Type type, out Type underlyingType) {
underlyingType = Nullable.GetUnderlyingType(type);
return underlyingType != null;
}
public static Type GetNullable(Type type) {
Type underlyingType;
return IsNullable(type, out underlyingType) ? type : NullableTypesCache.Get(type);
}
public static bool IsExactOrNullable(this Type type, Func<Type, bool> predicate) {
Type underlyingType;
if(IsNullable(type, out underlyingType))
return IsExactOrNullable(underlyingType, predicate);
return predicate(type);
}
public static bool IsExactOrNullable<T>(this Type type)
where T : struct {
return IsExactOrNullable(type, t => Equals(t, typeof(T)));
}
}
The usage:
Type type = typeof(int).GetNullable();
Console.WriteLine(type.ToString());
if(type.IsNullable())
Console.WriteLine("Type is nullable.");
Type underlyingType;
if(type.IsNullable(out underlyingType))
Console.WriteLine("The underlying type is " + underlyingType.Name + ".");
if(type.IsExactOrNullable<int>())
Console.WriteLine("Type is either exact or nullable Int32.");
if(!type.IsExactOrNullable(t => t.IsEnum))
Console.WriteLine("Type is neither exact nor nullable enum.");
Output:
System.Nullable`1[System.Int32]
Type is nullable.
The underlying type is Int32.
Type is either exact or nullable Int32.
Type is neither exact nor nullable enum.
PS. The NullableTypesCache is defined as follows:
static class NullableTypesCache {
readonly static ConcurrentDictionary<Type, Type> cache = new ConcurrentDictionary<Type, Type>();
static NullableTypesCache() {
cache.TryAdd(typeof(byte), typeof(Nullable<byte>));
cache.TryAdd(typeof(short), typeof(Nullable<short>));
cache.TryAdd(typeof(int), typeof(Nullable<int>));
cache.TryAdd(typeof(long), typeof(Nullable<long>));
cache.TryAdd(typeof(float), typeof(Nullable<float>));
cache.TryAdd(typeof(double), typeof(Nullable<double>));
cache.TryAdd(typeof(decimal), typeof(Nullable<decimal>));
cache.TryAdd(typeof(sbyte), typeof(Nullable<sbyte>));
cache.TryAdd(typeof(ushort), typeof(Nullable<ushort>));
cache.TryAdd(typeof(uint), typeof(Nullable<uint>));
cache.TryAdd(typeof(ulong), typeof(Nullable<ulong>));
//...
}
readonly static Type NullableBase = typeof(Nullable<>);
internal static Type Get(Type type) {
// Try to avoid the expensive MakeGenericType method call
return cache.GetOrAdd(type, t => NullableBase.MakeGenericType(t));
}
}
