[QoI] Confusing `__setitem__` method is failing with a "must be mutable" error about mojo

[lattner]

The error message is not great at all, but the problem is that the compiler cannot resolve the setitem parameter "idx" so it doesn't see the setitem overload. That's why it is complaining about not being mutable. I'll take a look at the error message

[lattner]

Thank you for reporting this, we now produce:

x.mojo:7:8: error: invalid call to '__setitem__': could not deduce parameter 'idx' of callee '__setitem__'
    lst[0] = 0
       ^
x.mojo:4:8: note: function declared here
    fn __setitem__[idx: Int](inout self, value: Int): pass
       ^

[leandrolcampos]

Hello, @lattner. Thank you so much for taking a look at this.

Considering that you closed the issue, I got the impression that the problem I reported was only with the error message. I couldn't understand why, in this case, it is expected that the compiler cannot resolve the setitem parameter "idx" so it doesn't see the setitem overload. What is the difference between this setitem and, for example, the setitem of the StaticTuple struct?

@always_inline("nodebug")
fn __setitem__[index: Int](inout self, val: Self.element_type): ...

All the best,