C ＃: in, out, ref keywords

One 、in keyword

in  Keywords cause parameters to be passed by reference , But make sure that the parameters are not modified . It makes a formal parameter an alias for an argument , This must be a variable . from C++ perspective ,in Keywords are a bit like const T&

1.in Modifier value type

1） When in When decorating basic data types , We cannot modify the value of basic data type , Can only read .

    void SetValue(in int i)
    {
        i = 4;// Report errors 
    }

2） When modified struct Data types can only be read .

public struct ValueType
{
    public int i;

    public void Set()
    {
        i = 1;
    }
}
public class ReadOnlyTest : MonoBehaviour
{
    ValueType valueType = new ValueType();
    void Seti2(in ValueType valtype)
    {
        valtype.i = 4;// Report errors 
    }
}

 

2.in Decorate reference types

Reference types are more flexible , It can modify the value of the member variable of the reference type .

public class RefType
{
    public int i = 0;
}
public class ReadOnlyTest : MonoBehaviour
{
    RefType refType = new RefType();
    void Seti1(RefType reftype)
    {
        reftype.i = 4;// It can be modified normally 
    }
}

3. Use... In functions in Keywords can be overloaded .

    void SetValue(in int i)
    {
        Debug.Log(i);
    }
    void SetValue(int i)
    {
        Debug.Log(i);
    }
    void Start()
    {
        SetValue(i);
        SetValue(in i);
    }

This part refers to ：in Parameter modifiers - C# Reference resources | Microsoft Docs

Two 、out keyword

out Key words follow in It's like , Basically like a couple . But for out For keywords, it can not only read , It can also be assigned , along with it Must be assigned .

    void SetValue(out int i)
    {
        i = 9;
        int k=i;
    }
    void Start()
    {
        int i = 0;
        SetValue(out i);
        Debug.Log(i);// Will print 9
    }

3、 ... and 、ref keyword

1. Official tips

1） In some cases , Accessing values by reference avoids potentially costly replication operations , To improve performance .

2） Don't confuse the concept of passing by reference with the concept of reference type . These two concepts are different . Whether the method parameter is a value type or a reference type , Can be by  ref  modify . When passed by reference , Value types are not boxed .

2.ref Modifier value type

ref It mainly affects the value type , Its modifier function shape participates in and out There's no big difference .

But what is more interesting is that it can directly modify variables . This is really like C++ The lvalue reference of is exactly the same .

    void Start()
    {
        int i = 0;
        ref int k = ref i;
        k = 3;
        Debug.Log(i);//i=3
    }

And you can also follow readonly Use keywords together

    void Start()
    {
        int i = 0;
        ref readonly int k = ref i;
        k = 3;// Read only , Non assignable , Report errors 
        Debug.Log(i);
    }

3.ref、in、out The difference between keywords

1） Pass on to  ref  or  in  Arguments of formal parameters must be initialized first , Then you can pass . This requirement is consistent with  out  The shape parameters are different , Before delivery , There is no need to explicitly initialize the arguments of this formal parameter .

This part refers to ：ref keyword - C# Reference resources | Microsoft Docs