Migrating to v19.0.0

CsvHelper 19 completes the mapping of constructor parameters that 18 started: a parameter takes the same configuration as a member, with attributes on the parameter or with Parameter in a class map. A few names changed on the way: TypeConverterOptions.NumberStyle is NumberStyles, MapTypeConverterOption is MemberMapTypeConverterOption, and a parameter map's Data.Name is Data.Names. The package depends on Microsoft.Bcl.HashCode on .NET Framework 4.7 and .NET Standard 2.0.

Constructor parameters

[BooleanFalseValues], [BooleanTrueValues], [Constant], [CultureInfo], [DateTimeStyles], [Default], [Format], [HeaderPrefix], [Ignore], [NameIndex], [NullValues], [NumberStyles], [Optional] and [TypeConverter] can go on a constructor parameter now, as [Name] and [Index] could in 18:

public class Order
{
    public Order(
        int id,
        [Name("Ordered On"), Format("yyyyMMdd")] DateTime orderedOn,
        [Optional, Default(1)] int quantity,
        [Ignore] string note)
    {
        // ...
    }
}

A class map configures them the same way, with methods like a member map's: Name, NameIndex, Index, Ignore, Default, Constant, Optional, TypeConverter and TypeConverterOption:

public class Order
{
    public Order(int id, DateTime orderedOn, int quantity, string note)
    {
        // ...
    }
}

public class OrderMap : ClassMap<Order>
{
    public OrderMap()
    {
        Parameter("id");
        Parameter("orderedOn").Name("Ordered On").TypeConverterOption.Format("yyyyMMdd");
        Parameter("quantity").Optional().Default(1);
        Parameter("note").Ignore();
    }
}

• Every parameter gets a value, since the constructor needs one: a constant parameter gets the constant, and an ignored one gets its Default, else the parameter's default value, else default.
• Types: ParameterMap.Default and Constant take a value of the parameter's type, and throw ArgumentException for another type.
• Your own attributes implement IParameterMapper, or IParameterReferenceMapper for a parameter whose type is mapped as a reference.

Class maps

The non-generic MemberMap, which MemberMaps.Find returns, no longer has Default(string). A string now goes to Default(object), which throws ArgumentException when the member isn't a string. The code compiles, and fails when the map is created. Pass a value of the member's type:

public class Foo
{
    public int Id { get; set; }
}

public class FooMap : ClassMap<Foo>
{
    public FooMap()
    {
        AutoMap(CultureInfo.InvariantCulture);
        MemberMaps.Find<Foo>(m => m.Id).Default("0");
    }
}

public class Foo
{
    public int Id { get; set; }
}

public class FooMap : ClassMap<Foo>
{
    public FooMap()
    {
        AutoMap(CultureInfo.InvariantCulture);
        MemberMaps.Find<Foo>(m => m.Id).Default(0);
    }
}

MemberMap<TClass, TMember>, which Map(m => m.Id) returns, keeps Default(string).

Type converter options

TypeConverterOptions.NumberStyle is NumberStyles, in the options cache and in your type converters:

var config = new CsvConfiguration(CultureInfo.InvariantCulture);
config.TypeConverterOptionsCache.GetOptions<decimal>().NumberStyle = NumberStyles.Currency;

var config = new CsvConfiguration(CultureInfo.InvariantCulture);
config.TypeConverterOptionsCache.GetOptions<decimal>().NumberStyles = NumberStyles.Currency;