Question

In probably the best error message I’ve gotten in awhile, I’m curious as to what went wrong.

The original code

float currElbowAngle = LeftArm ? Elbow.transform.localRotation.eulerAngles.y 
                               : 360f - Elbow.transform.localRotation.eulerAngles.y

I’m using Unity3d and C#; LeftArm is a bool type and according to documentation Elbow.transform.localRotation.eulerAngles.y returns a float value.

This code gives me the error :

There exists both implicit conversions from ‘float’ and ‘float’ and
from ‘float’ to ‘float’

This fixes it:

float currElbowAngle = LeftArm ? (float) Elbow.transform.localRotation.eulerAngles.y 
                               : 360f - Elbow.transform.localRotation.eulerAngles.y

So my question is this: What was that error trying to communicate and what actually went wrong?

Update 1: Elbow is a GameObject and this error is in Visual Studio

Answer 1

The ternary (e?a:b) operator is slightly trickier for the type system, because both sides need to give the same return type. I wouldn’t be surprised if there were a subtle bug there. It’s good that compliers make us laugh once in a while.

This probably fixes it too:

float currElbowAngle = LeftArm ? 0.0f + Elbow.transform.localRotation.eulerAngles.y 
                               : 360f - Elbow.transform.localRotation.eulerAngles.y

I’m speculating that the trouble is that your true branch is an lvalue and the false branch is an rvalue. My workaround makes both branches an rvalue.