Format currency with custom currency code (ASP.NET Core MVC)

Question

I am developing a ASP.NET Core MVC 1.1 application and I am struggling to find a clean and efficient solution for formatting decimal as currency with custom currency code (ie different than specified in the CultureInfo ).

Currently, I have the following decimal extension class:

public static class DecimalExtensions
{
  public static readonly Dictionary<string, string> CurrencyCodeToSymbol = new Dictionary<string, string>() {
    { "EUR", "€"},
    { "USD", "$"},
    { "GBP", "£"},
  };

  public static string FormatCurrency(this decimal decimalValue, string currencyCode)
  {
    var culture = (CultureInfo) CultureInfo.CurrentCulture.Clone();
    culture.NumberFormat.CurrencySymbol = CurrencyCodeToSymbol[currencyCode];
    return decimalValue.ToString("C", culture);
  }
}

My current solution consists of two parts:

1. Mapping from currency code to currency symbol.
2. Creating a new CultureInfo instance with the right CurrencySymbol property.

Sadly, I don't like either part.

For the first part, I could put the mapping into appsettings.json and fill the Dictionary in the Startup class. However, I would still prefer to skip this altogether and iterate over system supported cultures and currencies. However, as I have done my research, this is not yet possible in ASP.NET Core MVC 1.1.

For the second part, I don't like the Clone() part at all. Since the CultureInfo.CurrentCulture is readonly, I will probably have to clone it at some point, but preferably not at each call to my extension method.

Is there any way to cache the cloned and altered CultureInfo ? Since this is an extension class, I guess Dependency Injection is out of the picture.

Answer 1

If you are still looking for an answer, I've tweaked your extension method to cache the cloned culture info objects.

public static class DecimalExtensions
{
    private static readonly IDictionary<String, String> _currencyCodeToSymbol = new Dictionary<String, String>
    {
        { "EUR", "€"},
        { "USD", "$"},
        { "GBP", "£"},
    };

    private static readonly ConcurrentDictionary<String, CultureInfo> _currencyCodeToLocale =
        new ConcurrentDictionary<String, CultureInfo>();

    public static String FormatCurrency(this Decimal decimalValue, String currencyCode = "USD")
    {
        if (!_currencyCodeToSymbol.ContainsKey(currencyCode))
        {
            throw new NotImplementedException($"Currency code {currencyCode} is not supported");
        }

        var cultureInfo = _currencyCodeToLocale.GetOrAdd(currencyCode, _ =>
        {
            var info = CultureInfo.CurrentCulture.Clone() as CultureInfo;
            info.NumberFormat.CurrencySymbol = _currencyCodeToSymbol[currencyCode];
            return info;
        });

        return decimalValue.ToString("C", cultureInfo);
    }
}