declaration_order.cs

// boom
public class Ex
{
  public static readonly Ex Foo = Parse('f');
  public static readonly Ex Bar = Parse('b');

  Dictionary<char, string> validValues = new Dictionary<char, string>
  {
    { 'f', "Foo" },
    { 'b', "Bar" },
  };

  static Ex Parse(char value)
  {
    if (!validValues.ContainsKey(value))
      throw new InvalidOperationException("Bad value");
    
    return new Ex(value);
  }

  char value;

  private Ex(char value)
  {
    this.value = value;
  }
}


// fine :)
public class Ex
{
  Dictionary<char, string> validValues = new Dictionary<char, string>
  {
    { 'f', "Foo" },
    { 'b', "Bar" },
  };

  public static readonly Ex Foo = Parse('f');
  public static readonly Ex Bar = Parse('b');

  static Ex Parse(char value)
  {
    if (!validValues.ContainsKey(value))
      throw new InvalidOperationException("Bad value");
    
    return new Ex(value);
  }

  char value;

  private Ex(char value)
  {
    this.value = value;
  }
}