redux-sac/src/cow-value-model.js

export const cowValueModel = (key, keys = key.split('.')) => {
    function setField (x = {}, index, val) {
        if (index >= keys.length) return val;
        const key = keys[index],
            value = x[key],
            modified = setField(value, index + 1, val);
        return value === modified ? x : {...x, [key]: modified};
    }

    return {
        key,
        get (obj) {
            return keys.reduce((x = {}, key) => x[key], obj);
        },
        set (obj, val) {
            return setField(obj, 0, val);
        }
    };
};