Hi, do you have a link to the reddit article, so I can have a read? Thanks
On Wed, Apr 30, 2014 at 8:33 AM, Noam Yorav-Raphael <[email protected]>wrote: > Hi, > > I had a bug caused by a function mutating its arguments, and it had > occurred to me that it may be a good idea if rust would require a "mut" > prefix in that case. I asked on reddit, and was referred to this thread: > https://mail.mozilla.org/pipermail/rust-dev/2014-January/007670.html > > In the above message, Patrick shows a few examples which show that it's > hard to come up with rules on which arguments should be prefixed by "mut" > that will be sound and complete. I have an idea which may be. The idea is > to not look at function arguments but at uses of a variable. Here's a rule: > > Whenever a variable which was declared with "let mut" is being used in a > way that would have been illegal have it not been declared with "let mut", > it should be prefixed by "mut", unless it's obvious from the context that > it has to be mutable. > > I think it's quite simple and says exactly what should be the rules in > Patrick's examples. What's not well-defined is the "obvious from the > context" part. Certainly when a variable is on the left hand side of an > assignment there would be no need for "mut" annotation, as well as when > it's being prefixed by "&mut". I don't know if there are other cases. > > (If you're interested in the bug: I had to use a function solve(A, b) > which gets a matrix A and a vector b and returns a vector x such that Ax=b. > It does Gauss elimination, and for efficiency it modified A and b instead > of allocating new arrays. I used it like x = solve(A, b) and then used A > again. It was in Fortran, so the arguments A and b were annotated as being > "in out", but of course it didn't stop my perfectly looking function from > having a hidden bug.) > > What do you think? > Noam > > _______________________________________________ > Rust-dev mailing list > [email protected] > https://mail.mozilla.org/listinfo/rust-dev > >
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