C#•5mo ago

A small help in understanding structs:

I am learning how to use structs and have a question. for this question I decided to write a small test program by using some structs.
Inside Program.cs

c#
using System;
using static TestStuff.Class2;

namespace TestStuff
{
    internal class Program
    {
        static void Main(string[] args)
        {
            var testHoldStruct = new TestHold();
            var testHoldStruct2 = new TestHold2();

            testHoldStruct.val1 = 100;
            testHoldStruct.val2 = 500;

            testHoldStruct2.val2_1 = 1000;
            testHoldStruct2.val2_2 = 5000;

            Class1.ProcessTest(testHoldStruct, testHoldStruct2);

            Console.WriteLine("");
            Console.WriteLine("Done");
            Console.ReadLine();
        }
    }
}

c#
using System;
using static TestStuff.Class2;

namespace TestStuff
{
    internal class Program
    {
        static void Main(string[] args)
        {
            var testHoldStruct = new TestHold();
            var testHoldStruct2 = new TestHold2();

            testHoldStruct.val1 = 100;
            testHoldStruct.val2 = 500;

            testHoldStruct2.val2_1 = 1000;
            testHoldStruct2.val2_2 = 5000;

            Class1.ProcessTest(testHoldStruct, testHoldStruct2);

            Console.WriteLine("");
            Console.WriteLine("Done");
            Console.ReadLine();
        }
    }
}

Inside Class1.cs file:

c#
using System;
using static TestStuff.Class2;

namespace TestStuff
{
    internal class Class1
    {
        public static void ProcessTest(TestHold testHoldStruct, TestHold2 testHold2Struct)
        {
            Console.WriteLine(testHoldStruct.val1);
            Console.WriteLine(testHoldStruct.val2);

            Console.WriteLine(testHold2Struct.val2_1);
            Console.WriteLine(testHold2Struct.val2_2);
        }
    }
}

c#
using System;
using static TestStuff.Class2;

namespace TestStuff
{
    internal class Class1
    {
        public static void ProcessTest(TestHold testHoldStruct, TestHold2 testHold2Struct)
        {
            Console.WriteLine(testHoldStruct.val1);
            Console.WriteLine(testHoldStruct.val2);

            Console.WriteLine(testHold2Struct.val2_1);
            Console.WriteLine(testHold2Struct.val2_2);
        }
    }
}

Inside Class2.cs file:

c#
namespace TestStuff
{
    internal class Class2
    {
        public struct TestHold
        {
            public int val1;
            public int val2;
        }

        public struct TestHold2
        {
            public int val2_1;
            public int val2_2;
        }
    }
}

c#
namespace TestStuff
{
    internal class Class2
    {
        public struct TestHold
        {
            public int val1;
            public int val2;
        }

        public struct TestHold2
        {
            public int val2_1;
            public int val2_2;
        }
    }
}

Am I correct in assuming that when I am calling ProcessTest method from Program.cs file, a copy of the struct object is created in memory when Class1 is being processed ? I assume that if I use a class instead of a struct for ProcessTest method, I would only be passing it as a reference to the class object and in that case, a copy of the object isn't created when Class1 is being processed

7 Replies

Kouhai ／人◕ ‿‿ ◕人＼•5mo ago

Yes the struct is copied

MODiX•5mo ago

Kouhai ／人◕ ‿‿ ◕人＼

REPL Result: Success

var s = new TestStruct() {val = 10};
var c = new TestClass() {val = 10};
Inc(c, s);
Console.WriteLine(s.val);
Console.WriteLine(c.val);
void Inc(TestClass c, TestStruct s)
{
    c.val++;
    s.val++;
}
struct TestStruct { public int val; }
class TestClass { public int val; }

var s = new TestStruct() {val = 10};
var c = new TestClass() {val = 10};
Inc(c, s);
Console.WriteLine(s.val);
Console.WriteLine(c.val);
void Inc(TestClass c, TestStruct s)
{
    c.val++;
    s.val++;
}
struct TestStruct { public int val; }
class TestClass { public int val; }

Console Output

10
11

10
11

Compile: 467.630ms | Execution: 40.203ms | React with ❌ to remove this embed.

Kouhai ／人◕ ‿‿ ◕人＼•5mo ago

You can see here that val for TestClass was modified because it was passed by by reference

Surihia•5mo ago

Is there a performance hit by doing it like this ? would classes be a better option for this type of program ?

Kouhai ／人◕ ‿‿ ◕人＼•5mo ago

Depends on what you're going to do, if you're gonna box it a lot or you want the type to be mutable then go with a class, if not then a struct would be good. Also it's recommended to keep the structs below 16 bytes.

Surihia•5mo ago

what do you mean by box it ?

Kouhai ／人◕ ‿‿ ◕人＼•5mo ago

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/types/boxing-and-unboxing

Boxing and Unboxing - C# Programming Guide - C#

Learn about boxing and unboxing in C# programming. See code examples and view additional available resources.

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A small help in understanding structs: