bug in grammar with ?:

[Brett]

On Tuesday, 17 September 2019 at 18:06:55 UTC, ketmar wrote:
> Brett wrote:
>
>> Fails(loop is not taken):
>>
>> for(ulong i = len - 1; i >= (true) ? 0 : 1; i--)
>>
>>
>> passes
>>
>> for(ulong i = len - 1; i >= ((true) ? 0 : 1); i--)
>>
>> Only difference is parenthesis(yes, that is all, doesn't 
>> matter if it's true or false)
>
> not a bug. the whole thing before `?` is a condition, so
>
> 	i >= (true) ? 0 : 1
>
> returns 0, of course, because `i >= 1` (your `len` is obviously
> >= 1), and the result of the expression is therefor 0.

Makes sense, seems bad though... can introduce severe bugs in 
code if allowed. While using ?: there is not such a common idiom, 
using >= (or <= is)

Might be better for the compiler to detect such things and give a 
warning to use parenthesis? It could introduce subtle and hard to 
detect bugs.

Probably 99% of for loops use the syntax of var >= ...

I use it so much that way that I always think of ... as it's own 
expression rather than the entire part being an expression... 
it's my fault but I imagine 95% of programmers also think along 
similar ways. All it takes is forgetting this one time and one 
could have serious bugs(if the condition is complex and resolves 
in a hard to detect way it could produce such cases, rare but 
possible).