Proposal: side-effect free getters It's a pretty ...

# language-proposals

[JP Sugarbroad]

Proposal: side-effect free getters

It's a pretty well-known problem that if you split a project into multiple modules, you lose some smart casting because the compiler cannot assume that a getter in another module will always return the same result. I'd like to propose adding an annotation that indicates that the library author intends for a getter to remain side-effect free so that clients can write code more naturally. Thoughts?

[Ruckus]

Could you elaborate on this? I was under the impression that a custom getter always blocked smart casting, even in the same module. Also, the getter doesn't need to be side effect free for it to return different values each time (unless I misunderstand what you mean by side effect).

[JP Sugarbroad]

I mean it returns the same value every time unless you call something else on the object (e.g. a setter)

[JP Sugarbroad]

This would be an annotation on the property.

[JP Sugarbroad]

It would be useful for custom getters too!

[Ruckus]

Ah, I misread and thought you were talking about custom getters. Sorry about that.

[JP Sugarbroad]

Not at all! Useful clarification.

[rnett]

I think this would be an excellent feature, but IMO it should be done using contracts rather than a bespoke annotation

[JP Sugarbroad]

But how would one attach a contract to a generated getter?

[ephemient]

https://youtrack.jetbrains.com/issue/KT-8819/Smart-casts-for-immutable-properties-of-data-classes-even-public-ones

[JP Sugarbroad]

Not sure if that covers everything, but it's definitely a starting point!

[JP Sugarbroad]

Am curious if anyone has ideas on how one could attach a contract to a generated function (i.e. a function that doesn't have a body in the code)

[ephemient]

I don't think this would be handled by a contract anyway, at least in the current design. they feel very per-call

[ephemient]

there is a new design which isn't in the body https://youtrack.jetbrains.com/issue/KT-56127/K2-Provide-new-stable-syntax-for-contracts

[ephemient]

if that were how it works, then you can just contract the getter like how you can annotate the getter now