On Wednesday, 31 May 2023 at 09:14:49 UTC, Dom DiSc wrote:
On Wednesday, 31 May 2023 at 03:29:33 UTC, Cecil Ward wrote:
I have to admit that I don’t really understand immutable. I
have an idea that it could mean that an object has an address
in ROM, so its value will never change. Maybe const doesn’t
give you such a strong guarantee, disallows ‘you’ from
modifying it but others might do so, but who knows.
There are two perspectives: that of the value handed to a
function and that of the function taking the value.
"immutable" (or "mutable") is a property of the value, "const"
is a property of the function.
If the function can work with mutable values, but in fact
doesn't mutate them itself, it could also work with immutable
values. The fact that others could modify your "const" value
doesn't matter for immutable values, because they of course
can't be modified by others. For the function it doesn't
matter, because it only guarantees not to modify it itself,
don't care about what other can or can't do.
Without a guarantee as strong as the first idea I can’t really
understand how const can work properly. "You treat it as const
so do not modify it, but it might not be eternally fixed and
unchanging" that doesn’t seem to have enough value to me.
Why? What guarantee are you missing?
Your function can work with mutable data, so you don't care if
it can be modified also by others.
Now it happens that you doesn't modify the data. So why
shouldn't you be able to work on data that guarantees that it
also will not be changed by others? You don't care for such
modification anyway.
The meaning of "immutable" is: I cannot be modified. Not by you
and not by anybody else. It's a property of a value.
The meaning of "mutable" is: I can be modified by anybody. Work
with me only if that is ok for you. It's a property of a value.
The meaning of "const" is: I don't care if others modify the
data or not, I won't modify it myself. It's a property of a
function.
Dom, you explain it well. I’m just too stupid. Literally, as I’m
on strong pain drugs all the time, so things are a bit fuzzy. As
a professional C programmer for some years, I understood the word
const and used it all the time, as much as possible at every
opportunity, so I had some expectations. But the errors I’m
getting don’t fit in with the previous understanding I had with
the familiar ‘const’ keyword and make me think there must be
something else going on. So I will need to capture an example in
the wild, cage it and bring it in for scientific examination.
I can’t ask for an explanation of things going on that you can’t
inspect for yourself, obviously. And I don’t understand what the
problem is with using in as much as possible yet having to remove
it sometimes when something immutable is in use.
