Allocation-free generic conversions

GenericConversions.cs

using System.Numerics;

var variant = new Variant("42");

int i = variant.ConvertTo<int>();
float floatSum = variant.Add(10.0f);
int intSum = variant.Add(8);
double doubleProduct = variant.Multiply(2.5);
decimal decimalSum = variant.Add(100m);

static class GenericMath
{
    public static T Add<T, TVariant>(this TVariant value, T number) 
        where TVariant : struct, IConvertible<T>
        where T : INumber<T>
        => value.Convert() + number;

    public static T Multiply<T, TVariant>(this TVariant value, T number) 
        where TVariant : struct, IConvertible<T>
        where T : INumber<T>
        => value.Convert() * number;

    public static T Subtract<T, TVariant>(this TVariant value, T number) 
        where TVariant : struct, IConvertible<T>
        where T : INumber<T>
        => value.Convert() - number;

    public static T Divide<T, TVariant>(this TVariant value, T number) 
        where TVariant : struct, IConvertible<T>
        where T : INumber<T>
        => value.Convert() / number;
}

static class Conversions
{
    public static TTo ConvertTo<TTo>(this IConvertible<TTo> from)
        => from.Convert();   
}

interface IConvertible<out TTo>
{
    TTo Convert();
}

readonly struct Variant(string val) : IConvertible<int>, IConvertible<float>, IConvertible<double>, IConvertible<decimal>
{
    int IConvertible<int>.Convert() => Convert.ToInt32(val);   

    float IConvertible<float>.Convert() => Convert.ToSingle(val);  

    double IConvertible<double>.Convert() => Convert.ToDouble(val);

    decimal IConvertible<decimal>.Convert() => Convert.ToDecimal(val);
}