• JN (8/8) Aug 07 2018 int a, b;
• Steven Schveighoffer (16/28) Aug 07 2018 But operator precedence says that this is really:
• JN (5/23) Aug 07 2018 Ahhhh. I didn't think of that. Hmm, I guess a warning here would

JN <666total wp.pl> writes:

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?

Steven Schveighoffer <schveiguy gmail.com> writes:

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

JN <666total wp.pl> writes:

On Tuesday, 7 August 2018 at 19:58:40 UTC, Steven Schveighoffer 
wrote:
 On 8/7/18 3:18 PM, JN wrote:
 [...]

 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

Ahhhh. I didn't think of that. Hmm, I guess a warning here would 
be nice then, or perhaps DScanner could mark such cases as 
suspicious :)