Multiple return values. Methods in C# return only one value. This value can be an object with multiple fields. Several options are available for returning multiple values from a method.
If we need to return multiple values, we can use out parameters or return a type instance (like a tuple) containing all the values. We benchmark and compare approaches.
Example. There are many ways to return multiple parameters in the C# language. Modern versions of C# provide tuple syntax which are probably the most elegant.
Part 1 We can use formal "out" parameters. Once the method returns, we can read these values in the calling location.
Part 4 Older versions of the C# language support the Tuple class. We must specify the types as generic arguments.
Part 5 All the GetTwoNumbers methods return the same 2 ints. We verify this by printing the return values.
using System;
using System.Collections.Generic;
class Program
{
static void GetTwoNumbersA(out int number1, out int number2)
{
// Part 1: assign out parameters.
number1 = 1;
number2 = 2;
}
static KeyValuePair<int, int> GetTwoNumbersB()
{
// Part 2: return KeyValuePair.
return new KeyValuePair<int, int>(1, 2);
}
static (int, int) GetTwoNumbersC()
{
// Part 3: return tuple.
return (1, 2);
}
static Tuple<int, int> GetTwoNumbersD()
{
// Part 4: return Tuple class.
return new Tuple<int, int>(1, 2);
}
static void Main()
{
// Part 5: test all the methods and ensure their output is identical.
GetTwoNumbersA(out int number1, out int number2);
Console.WriteLine($"{number1} {number2}");
var resultB = GetTwoNumbersB();
Console.WriteLine($"{resultB.Key} {resultB.Value}");
var resultC = GetTwoNumbersC();
Console.WriteLine($"{resultC.Item1} {resultC.Item2}");
var resultD = GetTwoNumbersD();
Console.WriteLine($"{resultD.Item1} {resultD.Item2}");
}
}1 2
1 2
1 2
1 2
Benchmark. There are multiple ways to return multiple values from a method. The most common ones are probably out-parameters and KeyValuePair and tuples.
Version 1 This version of the code uses out parameters to return 2 values from a method.
Version 2 Here we use a KeyValuePair and read in its Key and Value properties from the returned method.
Version 3 A tuple can be used to return 2 values from a method. We access Item1 and Item2.
Result In 2024, using out parameters is a good performance tip—it performs the best in this benchmark.
using System;
using System.Collections.Generic;
using System.Diagnostics;
class Program
{
static void GetTwoNumbersA(out int number1, out int number2)
{
number1 = 1;
number2 = 2;
}
static KeyValuePair<int, int> GetTwoNumbersB()
{
return new KeyValuePair<int, int>(1, 2);
}
static (int, int) GetTwoNumbersC()
{
return (1, 2);
}
static void Main()
{
const int max = 100000000;
var s1 = Stopwatch.StartNew();
// Version 1: use 2 out parameters.
for (int i = 0; i < max; i++)
{
int a;
int b;
GetTwoNumbersA(out a, out b);
if (a + b != 3)
{
throw new Exception();
}
}
s1.Stop();
var s2 = Stopwatch.StartNew();
// Version 2: return KeyValuePair.
for (int i = 0; i < max; i++)
{
var pair = GetTwoNumbersB();
int a = pair.Key;
int b = pair.Value;
if (a + b != 3)
{
throw new Exception();
}
}
s2.Stop();
var s3 = Stopwatch.StartNew();
// Version 3: return tuple.
for (int i = 0; i < max; i++)
{
var tuple = GetTwoNumbersC();
int a = tuple.Item1;
int b = tuple.Item2;
if (a + b != 3)
{
throw new Exception();
}
}
s3.Stop();
Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / max).ToString("0.00 ns"));
Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000000) / max).ToString("0.00 ns"));
Console.WriteLine(((double)(s3.Elapsed.TotalMilliseconds * 1000000) / max).ToString("0.00 ns"));
}
}1.90 ns out
7.59 ns KeyValuePair
7.64 ns tuple
Summary. Multiple values can be returned from a method invocation. We used out to pass parameters by reference. With KeyValuePair and Tuple we returned multiple values in a container.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Oct 2, 2024 (new example).
