C# assignment problem

[Daniel-Brauer]

This code:

transform.position.y += floatHeight; //floatHeight is a float

…gives this error:

Cannot modify the return value of `UnityEngine.Transform.position’ because it is not a variable

The same code in Javascript doesn’t give me any trouble.

I’m new to C#. What am I missing?

[MatthewW]

Aras gave a great explanation in another thread:

@Aras Pranckevicius

Your initial approach does work in JavaScript. It does not work in C# though, because structs (and Vector3 is a struct) are always passed and returned by value. So the moment you write “transform.position” in C#, you get just a value back, it already does not know it comes from “transform.position”. Hence you need to copy it to temp. variable, change it, and assign it back.

So here you’ll need to do:

Vector3 posTemp = transform.position.
posTemp.y += floatHeight;
transform.position = posTemp;

[Daniel-Brauer]

Then why does this work:

transform.position += new Vector3(0.0f, floatHeight, 0.0f);

[NCarter_1]

Because the += operator reads the current value, does the addition, then assigns it back to transform.position. That’s allowed. The thing that isn’t allowed is editing part of a struct in a property.

[Daniel-Brauer]

Ok, thanks.