> On 17 Feb 2017, at 08:59, Nicolas Fezans via swift-evolution > <swift-evolution@swift.org> wrote: > > > Not only that, but even if you pass a value type as a parameter, that value > > type might have reference types as ivars. > > I think that arguments passed to a pure function shall be checked against > containing such references or objects that contains such references > themselves: I guess that this check could be made by the compiler. > Programmers will then have to see whether they choose a) to go to "pure > value-type arguments" (i.e. not containing directly nor indirectly such > references) and be able to declare some of their functions as pure or b) to > keep these references and not declare the corresponding functions as pure.
Wouldn't we need a way to declare value semantics? Array has such references but has value semantics so should be fine, no? > This seems to me to be the first and relatively easy way to solve this > problem. Later on I could imagine even that the compiler would be clever > enough to check whether the contained references are used (regardless of > whether it is just for a read access or also to mutate some values existing > outside the scope of the function itself) and if they are not used the purity > of the function could be validated also in that case. > > > Nicolas > > > >> On Fri, Feb 17, 2017 at 8:26 AM, Charles Srstka via swift-evolution >> <swift-evolution@swift.org> wrote: >> On Feb 16, 2017, at 1:27 PM, Sean Heber via swift-evolution >> <swift-evolution@swift.org> wrote: >> > >> > Doesn’t this break down if you can pass a reference as a parameter to a >> > pure function? If that’s not allowed, I guess I must have missed it. Also >> > this seems to require the function has a return value. I suppose generally >> > a pure function without a return value wouldn’t make much sense - unless >> > you pass it a reference. >> >> Not only that, but even if you pass a value type as a parameter, that value >> type might have reference types as ivars. So since any call to any reference >> type can potentially mutate it, and any call to any value type could call >> through to a reference type which might then be mutated, it does seem that >> purity is quite difficult to guarantee. >> >> Charles >> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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