ternary condition in laravel

I have to implement the remember me functionality, so i have to pass the value for $remember as a second argument in the Auth:attempt(); function. But the problem is when i am using this syntax for setting value in $remember, it display syntax error

$remember = isset($request->input('remember'))?true:false;
-------------------------------------------^//Expected: variable

But when i am using this syntax, it will not give any error

$remember = isset($request->remember)?true:false;

via Chebli Mohamed