What does Format("0.0".PadRight(100, '#') do when writing a CSV with CSVHelper

Question

I have a piece of code I am currently refactoring, but I can't find documentation about what a line in one of the ClassMaps is doing exactly. I try to get rid of the ClassMaps and replace them with attributes on the actual classes, but I'm unsure what would be the equivalent of this line.

This is (a simplified version of) the ClassMap I'm wondering about:

public class MyClassMap : ClassMap<MyCsvClass>
{
    public MyClassMap()
    {
        Map(t => t.MyNullableDoubleProperty).Name("MyCustomName").TypeConverterOption.Format("0.0".PadRight(100, '#'));
    }
}

I'm unsure about the TypeConverterOption part. My best guess is that it ensures that the output for the double property has a decimal point and at least one decimal place, but at most 100 additional decimal places. Is this correct? And more importantly: How can I do the same with an attribute for this property?

Answer 1

@OlivierJacot-Descombes already answered

What does the Format("0.0".PadRight(100, '#')) do?

so I'll answer

How can I do the same with an attribute?

You can use the FormatAttribute. Unfortunately, you can't use PadRight() in an attribute expression, so you would have to write out all of the # signs.

void Main()
{
    var records = new List<Foo> { new Foo { Id = 1, MyDouble = 2.0/3e50}};  
    using var csv = new CsvWriter(Console.Out, CultureInfo.InvariantCulture);   
    csv.WriteRecords(records);
}

public class Foo
{
    public int Id { get; set; }
    [Name("MyCustomName")]
    [Format("0.0#########################################################################################################################")]
    public double MyDouble { get; set; }
}

The other option would be to create a custom TypeConverter.

void Main()
{
    var records = new List<Foo> { new Foo { Id = 1, MyDouble = 2.0/3e50}};  
    using var csv = new CsvWriter(Console.Out, CultureInfo.InvariantCulture);   
    csv.WriteRecords(records);
}

public class Foo
{
    public int Id { get; set; }
    [Name("MyCustomName")]
    [TypeConverter(typeof(DoublePadRightConverter))]
    public double MyDouble { get; set; }
}

public class DoublePadRightConverter : DoubleConverter
{
    public override string ConvertToString(object value, IWriterRow row, MemberMapData memberMapData)
    {
        if (value is double d)
        {
            return d.ToString("0.0".PadRight(100, '#'), memberMapData.TypeConverterOptions.CultureInfo);
        }
        
        return base.ConvertToString(value, row, memberMapData);
    }
}