Compiler allows changing fields in getter functions

[jeshecdom]

Are you using the latest released (or pre-released, a.k.a. "next") version?

• I'm using the latest Tact version

Tact source code

extends mutates fun changeMe(self: Int) {
    self = 10;
}

contract Test {
    a: Int = 5;

    get fun changeFieldDirectly(): Int {
        self.a = 10;
        return self.a;
    }

    get fun changeFieldByCopyingContract(): Int {
        let contract_copy = self;
        contract_copy.a = 10;
        self = contract_copy;
        return self.a;
    }

    get fun changeFieldByMutatingFun(): Int {
        self.a.changeMe();
        return self.a;
    }
}

Relevant Tact/build system log output

No response

What happened?

In the above code, no error is reported, even though field self.a is being changed in three different ways in getter functions.

What did you expect?

An error stating that self.a or self cannot be assigned in getter functions. The semantics of getter functions state that they cannot change the contract state.

Steps to reproduce

No response

How do you run Tact?

Tact CLI

Anything else?

No response

[anton-trunov]

This is kind of handled for now in the Tact docs by saying this is "undefined behavior". Will be solved in the new typechecker

[Gusarich]

Do we really need to forbid that? Isn't it enough to just clarify that all made changes won't be applied (I'm sure it's already stated somewhere)

[anton-trunov]

Yeah, if it definitely dead code we should not allow that

[Gusarich]

Yeah, if it definitely dead code we should not allow that

what if someone wants to call a few state-modifying functions inside of a getter in order to calculate something to return?

[anton-trunov]

what if someone wants to call a few state-modifying functions inside of a getter in order to calculate something to return?

this is a very good point, let's see if we can address it or just delegate some dead code analysis to the misti static analyzer