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The `ref` keyword

Understand the different uses for the `ref` keyword and get more information on those uses

  • page csharp/language-reference/keywords/ref
  • updated 01/22/2026

You use the ref keyword in the following contexts:

  • In a method signature and in a method call, to pass an argument to a method by reference.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csPassByReference

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>
  • In a method signature, to return a value to the caller by reference. For more information, see ref return.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csReturnByReference

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>
  • In a declaration of a local variable, to declare a reference variable.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csLocalRef

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>
  • As the part of a conditional ref expression or a ref assignment operator.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csConditionalRef

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>
  • In a struct declaration, to declare a ref struct. For more information, see the ref structure types article.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csSnippetRefStruct

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>
  • In a ref struct definition, to declare a ref field. For more information, see the ref fields section of the ref structure types article.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csSnippetRefField

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>
  • In a generic type declaration to specify that a type parameter allows ref struct types.

    sample · csharpdocs/csharp/language-reference/keywords/snippets/refKeyword.csSnippetRefGeneric

    csharp
    public class RefKeywordExamples
{
    // <PassByReference>
    public void M(ref int refParameter)
    {
        refParameter += 42;
    }
    // </PassByReference>

    // <ReturnByReference>
    public ref int RefMax(ref int left, ref int right)
    {
        if (left > right)
        {
            return ref left;
        }
        else
        {
            return ref right;
        }
    }
    // </ReturnByReference>

    // <LocalRef>
    public void M2(int variable)
    {
        ref int aliasOfvariable = ref variable;
    }
    // </LocalRef> 

    // <ConditionalRef>
    public ref int RefMaxConditions(ref int left, ref int right)
    {
        ref int returnValue = ref left > right ? ref left : ref right;
        return ref returnValue;
    }
    // </ConditionalRef>
}

// <SnippetRefStruct>
public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}
// </SnippetRefStruct>

// <SnippetRefField>
public ref struct RefFieldExample
{
    private ref int number;
}
// </SnippetRefField>

// <SnippetRefGeneric>
class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}
// </SnippetRefGeneric>