Assignment in ternary condition operator

[Steven Schveighoffer]

On 8/7/18 3:18 PM, JN wrote:
> int a, b;
> 
> if (a = 3) { }   <- not allowed: Error: assignment cannot be used as a 
> condition, perhaps == was meant?
> 
> b = a = 3 ? 4 : 5   <- allowed
> 
> 
> I believe the second case should be disallowed also. It seems illogical, 
> that the first one isn't allowed, but the second one is, when the second 
> one is also 'assignment used as condition'. Is there a valid usecase for 
> such assignment?

But operator precedence says that this is really:

b = (a = (3 ? 4 : 5))

It's a different thing than the if statement. In the if statement, it's 
the *assignment* that is now the condition. Here, it is not an 
assignment that is the condition, but `3`. There is no common error that 
requires preventing assignment from the result of an assignment.

I realize that what you seeing is a typo from:

b = a == 3 ? 4 : 5

but the problem is that you are relying on precedence incorrectly here. 
If you type:

b = (a = 3) ? 4 : 5

Then you get the error. D can't solve all the problems. Best thing to do 
is to use parentheses to clarify what you want for your condition rather 
than rely on default order of operations.

-Steve