Function within another

Question

In Javascript, I can structure my code well by placing auxiliary functions inside other functions. For example:

I get something similar in C#? If not, how do you not leave the auxiliary functions "loose" in the project?

function Salva() {
    if(valida()) insereNoBanco();

    function valida() {
        // valida campos
    }

    function insereNoBanco() {
        // insere dados no banco
    }
}

Answer 1

In C# this was not possible (has in C# 7, see more in another question here). Enough to create delegates, but I doubt it’s what you want.

As a matter of fact, I see little use for it. Normally this will only be necessary if the code is too large and yet, the solution is not to create Inner functions, as shown in Javascript. This is done in JS because it is a language that has limitations to limit visibility and scope.

The idea of structuring parts of the code into separate functions is good, it separates responsibilities, but it doesn’t have to be within. Create other functions outside of it. The only drawback of this is that externally any other method in the class can call it. If it were internal, only it could call the function. But this is not usually a problem.

Of course you should create this function/method, such as private so it can’t be accessed outside the class.

public void Salva() => if (valida()) insereNoBanco();
private bool valida() {
    // valida campos
}
private void insereNoBanco() {
    // insere dados no banco
}

I wouldn’t do this but Daniel’s response put an example of what I initially said in the answer about lambda and which is the closest to the simulation of Inner fucntion used in Javascript:

public void Salva() {
    Func<bool> valida = () => {
        // valida campos
    };

    Action insereNoBanco = () => {
        // insere dados no banco
    };
    if (valida()) insereNoBanco();
}

I put in the Github for future reference.

It is unnecessary to do this, can have unwanted effects and is not idiomatic in C#.

Answer 2

In Javascript a function creates its own scope, and subfunctions inherit scopes.

In C#, scopes are defined by blocks (classes or methods), and are inherited by internal classes only.

An expression similar to his example would be the following:

internal static class Mae
{
    private static bool PodeSalvar = true;

    internal static void Salva()
    {

        Console.WriteLine(Filha.FilhaSalva); //Erro: Fora de escopo

        if (Filha.Valida()) Filha.InsereNoBanco();
    }

    internal static class Filha
    {
        private static bool FilhaSalva = false;

        internal static bool Valida()
        {
            return PodeSalvar; // Funciona, pois Filha herda o escopo de Mae
        }

        internal static void InsereNoBanco()
        {
            // insere dados no banco
        }
    }
}

Note that PodeSalvar is defined in the class Mae, and the method Valida() inner-class Filha has access to it, even if it has been defined as Private.

Meanwhile, FilhaSalva cannot be read by methods in the class Mae, even with a full descriptor (Filha.FilhaSalva) - since FilhaSalva is defined as Private.

Answer 3

You can declare functions within a method using lambda expressions:

Func<int, string> convertIntParaString = (num1) => num1.ToString();

Action<string, int> doisParamsSemRetorno = (str1, num1) =>
{
    str1.ToUpper();
    num1.ToString();
};

Using your code as an example:

void Salva() 
{
    Func<bool> valida = () => 
    {
        // valida campos
        return true;
    };

    Action insereNoBanco = () =>
    {
        // insere dados no banco
    };

    if(valida())
        insereNoBanco();
}

Answer 4

Ideal would be for you to create a support class containing the methods you need. So your code is more organized and easy to maintain. Below is a very simple example.

namespace Exemple
{
    public class Suporte
    {
        public static void Mensagem()
        {
            MessageBox.Show("Este é um método de apoio");
        }
    }
}

namespace Exemple
{
    public class Principal
    {
        public void ExibeMensagem()
        {
           Suporte.Mensagem();
        }
    }
}