mono/netcore/System.Private.CoreLib/shared/System/IFormattable.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

namespace System
{
    public interface IFormattable
    {
        string ToString(string? format, IFormatProvider? formatProvider);
    }
}