Swift 常数'；soda1和x27；推断为具有类型'；（）'；，这可能出乎意料

只是一个简单的小代码。它确实运行了，并输出了正确的结果，但我得到了一个错误：常量“soda1”推断为具有类型“（）”，这可能是意外的。我不知道怎么修。 试图编写一个简单的程序来输出一升苏打水的价格

func sodaoffer(type: String, price: Double, size: Double, amount: Double = 1) {
    let priceL = price / (size * amount)
    print("\(type) costs \(priceL) per liter")
}

let soda1 = sodaoffer(type: "Cola", price: 15, size: 1.5)
let soda2 = sodaoffer(type: "Fanta", price: 50, size: 0.5, amount: 4)
let soda3 = sodaoffer(type: "Faxe Kondi", price: 25, size: 2)

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您正在为变量分配一个返回（）或Void（这意味着什么都没有）的函数

试着归还一些东西：

func makeSodaOfferString(type: String, price: Double, size: Double, amount: Double = 1) -> String {
    let priceL = price / (size * amount)
    return "\(type) costs \(priceL) per liter)"
}

let sodaOffer1 = makeSodaOfferString(type: "Cola", price: 15, size: 1.5)
let sodaOffer2 = makeSodaOfferString(type: "Fanta", price: 50, size: 0.5, amount: 4)
let sodaOffer3 = makeSodaOfferString(type: "Faxe Kondi", price: 25, size: 2)

print(sodaOffer1)
print(sodaOffer2)
print(sodaOffer3)

您希望让soda1=sodaoffer（…）做什么？