Customize string comparisons

It is possible to generate StringComparer types for your Value Objects that wrap strings.

This is done by specifying the stringComparers parameter in either local or global config:

[ValueObject<string>(stringComparers: StringComparersGeneration.Generate)]
public partial class MyVo
{
}

This parameter is an enum with options Omit and Generate. It defaults to Omit.

If it's set to Generate, then it generates a bunch of comparers (Ordinal, IgnoreCase etc.) which can then be used in Equals or in collections, e.g.

        var left = MyVo.From("abc");
        var right = MyVo.From("AbC");

        var comparer = MyVo.Comparers.OrdinalIgnoreCase;

        left.Equals(right, comparer).Should().BeTrue();

... and in a dictionary

        Dictionary<MyVo, int> d = new(MyVo.Comparers.OrdinalIgnoreCase);

        MyVo key1Lower = MyVo.From("abc");
        MyVo key2Mixed = MyVo.From("AbC");

        d.Add(key1Lower, 1);
        d.Should().ContainKey(key2Mixed);

Also generated is an Equals method that takes an IEqualityComparer<>:

public bool Equals(MyVo other, IEqualityComparer<MyVo> comparer)
{
    return comparer.Equals(this, other);
}

As with strings, the Value Object itself doesn't change. GetHashCode is different for two objects with different strings if you don't specify a comparer.

MyString s1 = MyString.From("abc");
MyString s2 = MyString.From("ABC");

// different
s1.GetHashCode().Should.NotBe(s2.GetHashCode());

// same
s1.GetHashCode(StringComparison.OrdinalIgnoreCode).Should.Be(s2.GetHashCode(StringComparison.OrdinalIgnoreCode));

For storing in a dictionary, you can ask for an equality comparer, e.g.

Dictionary<MyString, int> d = new(MyString.EqualityComparerFor(StringComparison.OrdinalIgnoreCase))

Last modified: 12 September 2024