I am working with dart without allowing implicit dynamics and casts and I noticed the following:
When working with a local variable, I can use a type check on that variable and if the test passes, the compiler will just assume that I can use that variable as that type:
var emp; // set to something
if (emp is Person) {
// The compiler infers that emp is a person within this scope
// so it allows me to use Person's member functions and variables
// without the need for explicit typecast
// https://dart.dev/guides/language/language-tour#type-test-operators
emp.firstName = 'Bob';
}
However, this does not work if the variable is the member variable of an object:
class SuperPerson {
Object _emp;
/* Various things that could be doing things with _emp here */
void memberFun() {
if (_emp is Person) {
_emp.firstName = 'Bob'; // ERROR: The setter firstName is not defined for type Object.
(_emp as Person).firstName = 'Bob'; // workaround but would like to avoid casts that could fail.
}
}
}
Why is that and how can I overcome it? Could it be because of potentially other threads changing the value of _emp in between the test and the use?
