How to avoid duplicating string format with string interpolation

Question

Is it possible to not repeat the string format yyyy-MM-dd HH:mm:ss in:

Console.WriteLine($"{DateTime.Now:yyyy-MM-dd HH:mm:ss} {DateTime.Now.AddDays(1):yyyy-MM-dd HH:mm:ss}");

Other than with workarounds like:

Func<string, object, string> _ = string.Format;
var f = "yyyy-MM-dd HH:mm:ss";
Console.WriteLine($"{_(f, DateTime.Now)} {_(f, DateTime.Now.AddDays(1))}")

Answer 1

If you have many fragments to be formatted, I suggest implementing custom culture for this:

using System.Globalization;

...

public sealed class MyFormat : IDisposable {
  private CultureInfo m_Saved;
  private CultureInfo m_Current;

  public MyFormat() {
    m_Saved = CultureInfo.CurrentCulture;

    m_Current = new CultureInfo(m_Saved.Name, true);

    m_Current.DateTimeFormat.ShortDatePattern = "yyyy-MM-dd";
    m_Current.DateTimeFormat.LongTimePattern = "HH:mm:ss";

    //TODO: Add more formats' specifications here  

    CultureInfo.CurrentCulture = m_Current;
  }

  public void Dispose() {
    if (m_Current == CultureInfo.CurrentCulture) 
      CultureInfo.CurrentCulture = m_Saved;
  }
}

then you can put it as

using (new MyFormat()) {
  Console.WriteLine($"{DateTime.Now} {DateTime.Now.AddDays(1)}");
}