RuntimeStat.cs

using System.Collections.Generic;

namespace UnityRPG.Character.Stats
{
    public sealed class RuntimeStat
    {
        private readonly List<StatModifier> modifiers = new List<StatModifier>();

        public float BaseValue { get; }

        public float Value
        {
            get
            {
                float value = BaseValue;

                foreach (StatModifier modifier in modifiers)
                    value += modifier.Value;

                return value;
            }
        }

        public RuntimeStat(float baseValue)
        {
            BaseValue = baseValue;
        }

        public void AddModifier(StatModifier modifier)
        {
            if (modifier == null)
                return;

            modifiers.Add(modifier);
        }

        public void RemoveModifiersFromSource(object source)
        {
            modifiers.RemoveAll(modifier => ReferenceEquals(modifier.Source, source));
        }
    }
}