OpenXmlSimpleType children do not implement equality

Description

Classes like StringValue and HexBinaryValue do not implement equality and you must use their Value properties to compare them. This is not handy and can lead to unexpected results.

Information

• .NET Target: Any
• DocumentFormat.OpenXml Version: 2.8.1

Repro

using System.Collections.Generic;
using System.Linq;
using DocumentFormat.OpenXml;
using Xunit;

namespace DocumantFormat.OpenXml.Tests
{
    public class OpenXmlSimpleValueTests
    {
        private const string HexBinary = "12345678";
        private const string Value = "Hello World";

        [Fact]
        public void HexBinaryValue_ValuesAreEqual_HexBinaryValuesAreNotEqual()
        {
            var hexBinaryValue1 = new HexBinaryValue(HexBinary);
            var hexBinaryValue2 = new HexBinaryValue(HexBinary);

            Assert.Equal(hexBinaryValue1.Value, hexBinaryValue2.Value);

            // Those two HexBinaryValue instances should be deemed equal.
            Assert.NotEqual(hexBinaryValue1, hexBinaryValue2);
        }

        [Fact]
        public void HexBinaryValue_ValueIsContainedInList_ListDoesNotContainHexBinaryValue()
        {
            var hexBinaryValues = new List<HexBinaryValue>
            {
                new HexBinaryValue(HexBinary),
                new HexBinaryValue("ABCDEF00")
            };

            var hexBinaryValue = new HexBinaryValue(HexBinary);

            Assert.Contains(hexBinaryValue.Value, hexBinaryValues.Select(hbv => hbv.Value));

            // The HexBinaryValue should be deemed contained in the list.
            // The fact that this wasn't the case was a gotcha.
            Assert.DoesNotContain(hexBinaryValue, hexBinaryValues);
        }

        [Fact]
        public void StringValue_ValuesAreEqual_StringValuesAreNotEqual()
        {
            var stringValue1 = new StringValue(Value);
            var stringValue2 = new StringValue(Value);

            Assert.Equal(stringValue1.Value, stringValue2.Value);

            // The two StringValue instances should be deemed equal.
            Assert.NotEqual(stringValue1, stringValue2);
        }
    }
}

Observed

Two distinct instances of HexBinaryValue or StringValue, for example, will not be deemed equal even if their values are equal.

Expected

Given two distinct instances of HexBinaryValue, when the Value properties of those instances are equal, then those HexBinaryValue instances should be deemed equal as well.

The same should apply to other child classes of OpenXmlSimpleType such as StringValue.

[ThomasBarnekow]

Yes, can do.

[twsouthwick]

@ThomasBarnekow thanks for the contribution!