[dart-misc] Are getters and setters a bad idea? (discussion)

[Gonzalo Chumillas]

What do you think about getters and setters? I'm not talking about
traditional getters/setters methods (getXxx() and setXxx()). I'm talking
about the language construction. For example:

class MyClass {
String _str;
String get str => _str;
void set str(String value) {
_str = value;
}
}

I think they are "evil". The reason is why they are hiding valuable
information to the user. Specifically: information related to performance.
That is, let's consider the following innocuous code:

myVar.driveCpu = 100;

It actually calls the following method:

myVar.setMyDriveHardAndMyCpuHot(100);

Obviously, you don't want to call the previous method frequently. It may
compromise the system.
What do you think about this transcendental question? I'm not sure if using
accessor methods are good idea.

Thanks and sorry my awful English.

[Lex Berezhny]

If the setter is doing a lot more things than just setting a variable then
it's not a setter.​

Don't call `setMyDriveHardAndMyCpuHot()` inside of your setter and you'll
be fine.

['Bob Nystrom' via Dart Misc]

On Thu, Jun 23, 2016 at 9:08 AM, Gonzalo Chumillas <

Post by Gonzalo Chumillas
What do you think about getters and setters? I'm not talking about
traditional getters/setters methods (getXxx() and setXxx()). I'm talking
class MyClass {
String _str;
String get str => _str;
void set str(String value) {
_str = value;
}
}
I think they are "evil". The reason is why they are hiding valuable
information to the user. Specifically: information related to performance.
myVar.driveCpu = 100;
myVar.setMyDriveHardAndMyCpuHot(100);
Obviously, you don't want to call the previous method frequently. It may
compromise the system.
What do you think about this transcendental question? I'm not sure if
using accessor methods are good idea.

When you're using some API, you want your code to look clean and focused on
the domain of your program. If the object you're working with conceptually
has some properties you can modify or access, then getters and setters are
the natural syntax for that:

var bostonCream = new Doughnut();
bostonCream.filling = Filling.cremePatissiere;
bostonCream.topping = Topping.chocolate;
print(bostonCream.deliciousness); // 1000000.


Adding "get", "set" and "()" to every call is just pointless noise. It
makes you notice the programming language's machinery instead of thinking
about your program. In the above code, you want to think about *doughnuts*,
not Dart syntax. The syntax is just a means to an end.

In most cases, whether or not a "property" is a field or the result of some
computation is an implementation detail. It may be an implementation detail
with performance that is somewhat slower than a direct field access, but
that's OK. Dart is a high level language. Keep in mind that even adding two
numbers may involve heap allocation!

The absence of "()" is not a strong signal in Dart that "this thing is very
fast". That *is* a convention in other languages, and *could* *have* been
one in Dart, but we didn't pick that convention, and users shouldn't expect
it.

However, if the user of your API is more focused on the *work the operation
performs* than they are *the value passed in* or *the result returned*,
then in that case, a method is likely a better fit than a getter or setter.
Give the method an imperative name that describes the work being done. If
you find yourself naming it "get___" or "set___", then just use a getter or
setter.

If you name it "download___" or "send___" or "calculate___", or
"update___", then you're on the right path with a method.

Performance is *one* reason why they may want to focus on the work being
performed, but it's not the only one. A very fast operation that has a
visible side-effect might also be better as a method than a getter or
setter.

See also: https://www.dartlang.org/effective-dart/design/#members

Cheers!

– bob

[Gonzalo Chumillas]

Thanks! Your explanation was very instructive.