// Helpers/GetDeclaration
private static string GetTypeDeclaration(IEnumerable <string> keywords, string type, string? @base, IEnumerable <string>?interfaces)
{
var builder = new StringBuilder();
builder.AppendKeywords(keywords);
builder.Append(type);
builder.AppendValuesIfAny(" : ", null, Concat(@base, interfaces));
return(builder.ToString());
}