How Are Arrays and Lists Passed in C#: By Reference or By Value?

Passing by Reference in C#: Arrays and Lists

Many programming languages, including C#, provide reference types and value types. Regarding the passing mechanism of arrays and lists, a common question arises: are they passed by reference or by value by default?

Arrays and Lists in C#

In C#, arrays and lists are reference types. This means they are stored in the managed heap and referenced by pointers. When passing a reference type, the reference itself is passed by value.

Default delivery mechanism

Therefore, in C#, arrays and lists are passed by value by default. This passing mechanism means that any changes made within a method or function to the contents of a passed array or list will be reflected in the calling code. However, reassigning the passed array or list within a method or function will not be visible in the calling code.

Example

Consider the following code snippet:

<code class="language-csharp">void Foo(int[] data)
{
    data[0] = 1; // 更改数组内容，在调用代码中可见
}

void Bar(int[] data)
{
    data = new int[20]; // 重新分配数组，在调用代码中不可见
}</code>

Use pass-by-reference to optimize performance

In some cases, passing an array or list by reference can improve the performance of your program. This is because it avoids copying the entire data structure, which can be very expensive for large data sets.

To pass an array or list by reference, you can use the "ref" modifier when declaring function parameters. This modifier explicitly indicates that the reference itself will be passed by reference, not just its value.

Example

<code class="language-csharp">void Baz(ref int[] data)
{
    data[0] = 1; // 更改数组内容，在调用代码中可见
    data = new int[20]; // 重新分配数组，在调用代码中可见
}</code>

By using the "ref" modifier, changes to the contents and reassignments of the array in the "Baz" function will be visible in the calling code. Keep in mind that if you don't need to modify the reference itself in a method or function, it's generally recommended to avoid using the "ref" modifier, as it can lead to code confusion.

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