Getting weird compilation error

I want the camera to move in the forward direction but I want to keep the y position the same. So I wrote this:

if (walking) {
transform.position = transform.position + Camera.main.transform.forward * .5f * Time.deltaTime;
transform.position.y = .5f;
}

Yet I got:
Assets/scripts/cameraControl.cs(25,23): error CS1612: Cannot modify a value type return value of `UnityEngine.Transform.position'. Consider storing the value in a temporary variable

which indicates I can't set transform.position.y? What does it mean??

 

There are two ways to create complex data types in C#. One of them is the class you've undoubtedly been using this whole time but the other way to do it is via a struct. This problem is coming from the way structs are treated by C#.

When you retrieve an object through a property (or an indexer) that is a struct you are given a copy of the object rather than a reference to the object itself. Because it's a copy the actual object you're accessing isn't being stored and therefore can't be modified.

If you wish to modify the property, you first need to store the copy, then modify it, and then pass it back.

Code (csharp):

1. if (walking) {
2.     transform.position = transform.position + Camera.main.transform.forward * .5f * Time.deltaTime;
3.     Vector3 pos = transform.position;
4.     pos.y = 0.5f;
5.     transform.position = pos;
6. }

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-messages/cs1612

 

Thank you very very much!!!