Pemrograman fungsional bukan apa yang diperintahkan kepada kita

Pemrograman fungsional adalah paradigma yang sangat lucu. Di satu sisi, semua orang tahu tentang itu, dan semua orang suka menggunakan semua jenis pencocokan pola dan lambda, di sisi lain, beberapa orang biasanya menulis dalam bahasa FP murni. Oleh karena itu, pemahaman bahwa ini lebih cenderung untuk kembali ke mitos dan legenda perkotaan, yang sangat jauh dari kebenaran, dan orang-orang memiliki kesan bahwa "FP cocok untuk semua program perhitungan fraktal yang diisolasi dari kehidupan, tetapi untuk masalah nyata ada rekam jejak yang terbukti. dalam pertempuran OOP teruji waktu. "

Meskipun orang biasanya mengenali kenyamanan fitur FP, jauh lebih baik untuk menulis:

int Factorial(int n)
{
    Log.Info($"Computing factorial of {n}");
    return Enumerable.Range(1, n).Aggregate((x, y) => x * y);
}

int Factorial(int n)
{
    int result = 1;
    for (int i = 2; i <= n; i++)
    {
        result *= i;
    }
    return result;
}

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public class Cafe
{
    public Coffee BuyCoffee(CreditCard card)
    {
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    }
}

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{
    public Coffee BuyCoffee(CreditCard card, IPaymentProvider paymentProvider)
    {
        var cup = new Coffee()
        paymentProvider.Charge(card, cup.Price)
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    }
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public class Cafe
{
    public Coffee BuyCoffee(CreditCard card, IPaymentProvider paymentProvider)
    {
        var cup = new Coffee()
        paymentProvider.Charge(card, cup.Price)
        return cup
    }

    public Coffee[] BuyCoffees(int count, CreditCard card, IPaymentProvider paymentProvider)
    {
        //      0   , 
        //       0 
        if (count == 0) return Array.Empty<Coffee>(); 
        var cups = Enumerable.Range(0, count).Select(_ => new Coffee()).ToArray();
        paymentProvider.Charge(card, cups[0].Price * count)
        return cups
    }
}

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public class Cafe
{
    public (Coffee, Charge) BuyCoffee(CreditCard card)
    {
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    }
}

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public class Cafe
{
    public (Coffee, Charge) BuyCoffee(CreditCard card)
    {
        var cup = new Coffee()
        return (cup, new Charge(card, cup.Price))
    }

    public (Coffee[], Charge) BuyCoffees(int count, CreditCard card)
    {
        var (coffees, charges) = Enumerable.Range(0, count)
                                           .Select(_ => BuyCoffee(card))
                                           .Unzip();
        return (coffees, charges.Aggregate((c1, c2) => c1.ombine(c2))
    }
}

- Combine:

public class Charge
{
    public CreditCard Card { get; set; }
    public double Amount { get; set; }

    public Charge(CreditCard card, double amount)
    {
        Card = card;
        Amount = amount;
    }

    public Charge Combine(Charge other)
    {
        if (Card != other.Card) 
            throw new ArgumentException("Can't combine charges to different cards");
        return new Charge(Card, Amount + other.Amount);
    }
}

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    charges.GroupBy(x => x.Card).Select(g => g.Aggregate((c1, c2) => c1.Combine(c2))

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