シグネチャと戻り値、式形式、オプション／名前付き、ref／out、オーバーロード

メソッドの基礎

シグネチャと戻り値

using System;

public class MathUtil
{
  // Signature: name Add, parameters (int a, int b), return int
  public static int Add(int a, int b)
  {
    return a + b;
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    int s = MathUtil.Add(2, 3);
    Console.WriteLine("Sum = " + s);
  }
}

式形式メソッド

using System;

public static class FormatUtil
{
  // Expression-bodied method (C# 6): concise one-liner
  public static string Greet(string name) => "Hello, " + name + "!";
}

public class Program
{
  public static void Main(string[] args)
  {
    Console.WriteLine(FormatUtil.Greet("Ada"));
  }
}

オプション引数と名前付き引数

using System;

public static class Logger
{
  // Optional parameter: times has a default
  public static void Log(string message, int times = 1)
  {
    for (int i = 0; i < times; i = i + 1)
    {
      Console.WriteLine(message);
    }
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    Logger.Log("One time");                 // uses default
    Logger.Log(message: "Twice", times: 2); // named arguments
  }
}

ref と out の基礎

using System;

public static class RefOutDemo
{
  public static void Increment(ref int x)
  {
    x = x + 1; // modifies caller's variable
  }

  public static bool TryDivide(int a, int b, out int result)
  {
    if (b == 0)
    {
      result = 0;       // out must be assigned before return
      return false;
    }
    result = a / b;
    return true;
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    int n = 10;
    RefOutDemo.Increment(ref n);
    Console.WriteLine("n = " + n); // 11

    int r;
    bool ok = RefOutDemo.TryDivide(9, 0, out r);
    Console.WriteLine("ok=" + ok + " r=" + r);
  }
}

オーバーロードと注意点

using System;

public static class Calc
{
  // Overloads: same name, different parameter lists
  public static int Area(int side) { return side * side; }
  public static int Area(int width, int height) { return width * height; }

  // C# 6 has no local functions; use private helpers instead.
  private static int DoubleIt(int x) { return x + x; }

  public static int TwiceArea(int side)
  {
    int a = Area(side);
    return DoubleIt(a);
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    Console.WriteLine("Area square 3 = " + Calc.Area(3));
    Console.WriteLine("Area rect 3x4 = " + Calc.Area(3, 4));
    Console.WriteLine("Twice area of 3 = " + Calc.TwiceArea(3));
  }
}

ref と out のルール

まとめ