ComparerHelpers.cs

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namespace System.Collections.Generic;
 
internal static class ComparerHelpers
{
    internal static object CreateDefaultComparer(Type type)
    {
        object obj = null;
        RuntimeType runtimeType = (RuntimeType)type;
        if (typeof(IComparable<>).MakeGenericType(type).IsAssignableFrom(type))
        {
            obj = RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(GenericComparer<int>), runtimeType);
        }
        else if (type.IsGenericType)
        {
            if (type.GetGenericTypeDefinition() == typeof(Nullable<>))
            {
                obj = TryCreateNullableComparer(runtimeType);
            }
        }
        else if (type.IsEnum)
        {
            obj = TryCreateEnumComparer(runtimeType);
        }
        return obj ?? RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(ObjectComparer<object>), runtimeType);
    }
 
    private static object TryCreateNullableComparer(RuntimeType nullableType)
    {
        RuntimeType runtimeType = (RuntimeType)nullableType.GetGenericArguments()[0];
        if (typeof(IComparable<>).MakeGenericType(runtimeType).IsAssignableFrom(runtimeType))
        {
            return RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(NullableComparer<int>), runtimeType);
        }
        return null;
    }
 
    private static object TryCreateEnumComparer(RuntimeType enumType)
    {
        TypeCode typeCode = Type.GetTypeCode(Enum.GetUnderlyingType(enumType));
        if ((uint)(typeCode - 5) <= 7u)
        {
            return RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(EnumComparer<>), enumType);
        }
        return null;
    }
 
    internal static object CreateDefaultEqualityComparer(Type type)
    {
        object obj = null;
        RuntimeType runtimeType = (RuntimeType)type;
        if (type == typeof(byte))
        {
            obj = new ByteEqualityComparer();
        }
        else if (type == typeof(string))
        {
            obj = new GenericEqualityComparer<string>();
        }
        else if (type.IsAssignableTo(typeof(IEquatable<>).MakeGenericType(type)))
        {
            obj = RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(GenericEqualityComparer<string>), runtimeType);
        }
        else if (type.IsGenericType)
        {
            if (type.GetGenericTypeDefinition() == typeof(Nullable<>))
            {
                obj = TryCreateNullableEqualityComparer(runtimeType);
            }
        }
        else if (type.IsEnum)
        {
            obj = TryCreateEnumEqualityComparer(runtimeType);
        }
        return obj ?? RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(ObjectEqualityComparer<object>), runtimeType);
    }
 
    private static object TryCreateNullableEqualityComparer(RuntimeType nullableType)
    {
        RuntimeType runtimeType = (RuntimeType)nullableType.GetGenericArguments()[0];
        if (typeof(IEquatable<>).MakeGenericType(runtimeType).IsAssignableFrom(runtimeType))
        {
            return RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(NullableEqualityComparer<int>), runtimeType);
        }
        return null;
    }
 
    private static object TryCreateEnumEqualityComparer(RuntimeType enumType)
    {
        TypeCode typeCode = Type.GetTypeCode(Enum.GetUnderlyingType(enumType));
        if ((uint)(typeCode - 5) <= 7u)
        {
            return RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(EnumEqualityComparer<>), enumType);
        }
        return null;
    }
}