How To Test if Type is Primitive

From @Ronnie Overby response and @jonathanconway comment, I wrote this method that works for Nullable, and exclude user structs.

public static bool IsSimpleType(Type type)
{
    return
        type.IsPrimitive ||
        new Type[] {
            typeof(string),
            typeof(decimal),
            typeof(DateTime),
            typeof(DateTimeOffset),
            typeof(TimeSpan),
            typeof(Guid)
        }.Contains(type) ||
        type.IsEnum ||
        Convert.GetTypeCode(type) != TypeCode.Object ||
        (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>) && IsSimpleType(type.GetGenericArguments()[0]))
        ;
}

With the following TestCase :

struct TestStruct
{
    public string Prop1;
    public int Prop2;
}

class TestClass1
{
    public string Prop1;
    public int Prop2;
}

enum TestEnum { TheValue }

[Test]
public void Test1()
{
    Assert.IsTrue(IsSimpleType(typeof(TestEnum)));
    Assert.IsTrue(IsSimpleType(typeof(string)));
    Assert.IsTrue(IsSimpleType(typeof(char)));
    Assert.IsTrue(IsSimpleType(typeof(Guid)));

    Assert.IsTrue(IsSimpleType(typeof(bool)));
    Assert.IsTrue(IsSimpleType(typeof(byte)));
    Assert.IsTrue(IsSimpleType(typeof(short)));
    Assert.IsTrue(IsSimpleType(typeof(int)));
    Assert.IsTrue(IsSimpleType(typeof(long)));
    Assert.IsTrue(IsSimpleType(typeof(float)));
    Assert.IsTrue(IsSimpleType(typeof(double)));
    Assert.IsTrue(IsSimpleType(typeof(decimal)));

    Assert.IsTrue(IsSimpleType(typeof(sbyte)));
    Assert.IsTrue(IsSimpleType(typeof(ushort)));
    Assert.IsTrue(IsSimpleType(typeof(uint)));
    Assert.IsTrue(IsSimpleType(typeof(ulong)));

    Assert.IsTrue(IsSimpleType(typeof(DateTime)));
    Assert.IsTrue(IsSimpleType(typeof(DateTimeOffset)));
    Assert.IsTrue(IsSimpleType(typeof(TimeSpan)));

    Assert.IsFalse(IsSimpleType(typeof(TestStruct)));
    Assert.IsFalse(IsSimpleType(typeof(TestClass1)));

    Assert.IsTrue(IsSimpleType(typeof(TestEnum?)));
    Assert.IsTrue(IsSimpleType(typeof(char?)));
    Assert.IsTrue(IsSimpleType(typeof(Guid?)));

    Assert.IsTrue(IsSimpleType(typeof(bool?)));
    Assert.IsTrue(IsSimpleType(typeof(byte?)));
    Assert.IsTrue(IsSimpleType(typeof(short?)));
    Assert.IsTrue(IsSimpleType(typeof(int?)));
    Assert.IsTrue(IsSimpleType(typeof(long?)));
    Assert.IsTrue(IsSimpleType(typeof(float?)));
    Assert.IsTrue(IsSimpleType(typeof(double?)));
    Assert.IsTrue(IsSimpleType(typeof(decimal?)));

    Assert.IsTrue(IsSimpleType(typeof(sbyte?)));
    Assert.IsTrue(IsSimpleType(typeof(ushort?)));
    Assert.IsTrue(IsSimpleType(typeof(uint?)));
    Assert.IsTrue(IsSimpleType(typeof(ulong?)));

    Assert.IsTrue(IsSimpleType(typeof(DateTime?)));
    Assert.IsTrue(IsSimpleType(typeof(DateTimeOffset?)));
    Assert.IsTrue(IsSimpleType(typeof(TimeSpan?)));

    Assert.IsFalse(IsSimpleType(typeof(TestStruct?)));
}

I just found this question while looking for a similar solution, and thought you might be interested in the following approach using System.TypeCode and System.Convert.

It is easy to serialize any type that is mapped to a System.TypeCode other than System.TypeCode.Object, so you could do:

object PropertyValue = ...
if(Convert.GetTypeCode(PropertyValue) != TypeCode.Object)
{
    string StringValue = Convert.ToString(PropertyValue);
    ...
}

The advantage with this approach is you don't have to name every other acceptable non-primitive type. You could also modify the above code slightly to handle any type that implements IConvertible.

You can use the property Type.IsPrimitive, but be carefull because there are some types that we can think that are primitives, but they aren´t, for example Decimal and String.

Edit 1: Added sample code

Here is a sample code:

if (t.IsPrimitive || t == typeof(Decimal) || t == typeof(String) || ... )
{
    // Is Primitive, or Decimal, or String
}

Edit 2: As @SLaks comments, there are other types that maybe you want to treat as primitives, too. I think that you´ll have to add this variations one by one.

Edit 3: IsPrimitive = (Boolean, Byte, SByte, Int16, UInt16, Int32, UInt32, Int64, UInt64, IntPtr, UIntPtr, Char, Double, and Single), Anther Primitive-Like type to check (t == typeof(DateTime))

We do it like this in our ORM:

Type t;
bool isPrimitiveType = t.IsPrimitive || t.IsValueType || (t == typeof(string));

I know that using IsValueType is not the best option (you can have your own very complex structs) but it works in 99% cases (and includes Nullables).