CODEWITHSUNDEEP
c#unity-game-engine
hmtinc
hmtinc

Reputation: 43

Unity : Cannot modify a value type return value of `UnityEngine.Transform.position'

I am currently trying to lock my camera to a map I made in Unity3D using this code that was converted from JavaScript:

transform.position.z = Mathf.Clamp(transform.position.z, zmin, zmax);
transform.position.x = Mathf.Clamp(transform.position.x, xmin, xmax);

But Unity keeps on returning the following error while compiling: error CS1612: Cannot modify a value type return value of 'UnityEngine.Transform.position'. Consider storing the value in a temporary variable.

Upvotes: 3

Views: 13249

Answers (3)

afpro
afpro

Reputation: 1103

because Vector3 is a struct, means 'value type', not 'reference type'. so, the property Transform.position's getter return a 'NEW' Vector3 for result. if you modify it directly, the 'NEW' Vector3 is modified, 'NOT' the Transform.position property. is that clear?

Transform.position.x = 0; // this is wrong code
// is same with
Vector3 _tmp = Transform.position; // getter
_tmp.x = 0; // change 'NEW' Vector3

this is obviously NOT what you want, so compiler told you that's a problem.

you should declare a new Vector3, and init with Transform.position's getter, modify it, and change Transform.position with it's setter.

Vector3 _tmp = Transform.position; // getter
_tmp.x = 0; // change 'NEW' Vector3
Transform.position = _tmp; // change Transform.position with it's setter

don't worry about Vector3 _tmp, it's just value type, won't create memory fragmentations.

Upvotes: 11

Heisenbug
Heisenbug

Reputation: 39194

You can't modify the single coordinate of the position. You have to reassign the whole vector:

Vector3 newVal;
newVal.x = transform.position.x = Mathf.Clamp(transform.position.x, xmin, xmax);
...
transform.position = newVal;

Upvotes: 1

Valery Petrov
Valery Petrov

Reputation: 673

About Compiler Error CS1612

You shouldn't modify camera position that way.

Upvotes: 1

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