The difference between array and ref array

Sometimes you'll want to pass an object (like an array) into a method, and have that method update the object. For an array, the common ways to do this are using the ref keyword, or modifying a member of an array. It's easy to confuse these two approaches because if you're just updating a member, they appear to have the same affect. However they're actually fundamentally different - passing in an array by ref lets you modify the array reference itself, such as changing it to a new array with a new length. The code snippet below illustrates this:


#region Normal Array [TestMethod]
public void TestMethod1()
{ //Normal array changes individual member
string[] astr = new string[]{"aaa"};
ModifyArray1(astr);
Assert.AreEqual("bbb", astr[0]);
} [TestMethod]

public void TestMethod2()
{ //Non-ref array doesn't change array itself
string[] astr = new string[] { "aaa" };
ModifyArray2(astr); Assert.AreEqual(1, astr.Length);
Assert.AreEqual("aaa", astr[0]);
}
public static void ModifyArray1(string[] astr)
{
astr[0] = "bbb";
}
public static void ModifyArray2(string[] astr)
{ astr = new string[] { "ccc", "ccc" };
} #endregion

#region Ref Array [TestMethod]
public void TestMethodRef1()
{
string[] astr = new string[] { "aaa" };
ModifyArrayRef1(ref astr);
Assert.AreEqual("bbb", astr[0]);
}
[TestMethod]
public void TestMethodRef2()
{ //Ref array can change the array itself, like giving it a new length
string[] astr = new string[] { "aaa" };
ModifyArrayRef2(ref astr);
Assert.AreEqual(2, astr.Length);
Assert.AreEqual("ccc", astr[0]);
}
public static void ModifyArrayRef1(ref string[] astr)
{
astr[0] = "bbb";
}
public static void ModifyArrayRef2(ref string[] astr)
{ astr = new string[] { "ccc", "ccc" };
} #endregion