为了在这样的循环中更轻松地进行修改，您应该将Products设为一个类，因为它是通过引用传递的.另外，在Products中将quantities更改为var，并将解析代码替换为此:

For easier modification in loops like this, you should make Products a class, since it's passed by reference. Also, make quantities to a var in your Products and replace the parsing code to this:

for product in products.arrayValue {
    let productId = product["product_id"].stringValue

    let quantity = (sizeId: product["size_id"].stringValue,
                    quantity: product["quantity"].stringValue)

    if let product = self.productWithQuantites.filter({ $0.id == productId }).first {
        product.quantities?.append(quantity)
    } else {
        self.productWithQuantites.append(Products(id: productId, quantities: [quantity]))
    }
}

此代码将新的元组附加到现有产品的quantities属性，或者如果不存在，则创建新的Products并将其附加到productWithQuantites.

This code appends a new tuple to the quantities property of an existing product, or if it does not exist, it creates a new Products and appends that to productWithQuantites.