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| Subject | in/inout/out for arrays needs clear defining | ||||||||||||||||||
| From | Stewart Gordon <smjg_1998@yahoo.com> | ||||||||||||||||||
| Date | Tue, 06 Jul 2004 11:02:45 +0100 | ||||||||||||||||||
| Newsgroups | digitalmars.D,digitalmars.D.bugs | ||||||||||||||||||
Using DMD 0.94, Windows 98SE. I've long noticed a potential cause for confusion. The passing of arrays as (address, length) tuples, while sensible on the whole, leads to counter-intuitive behaviour. While it's logical to this form, it isn't what one might expect, and the spec doesn't clearly define the semantics of in/inout/out on arrays. In short: if an array is passed as in, someone might think that the contents of the array are in, when in reality only the (address, length) tuple is in; the actual array contents are inout. Of course, it's probably too late to clean up the semantics without breaking plenty of existing code. But I suppose the main point is that the semantics we have need to be clearly explained. Still, a possible idea for the future would be to allow the contents and dimensions to have separate in/inout/out settings. The idea I came up with a while back is a notation like void qwert(inout int[in] yuiop); meaning that the length is in, and the contents are inout. There would be six possibilities: in int[in] "Give me an array to look at" Pass in (address, length); either disallow changes to data in the function body, or copy on entry if any changes can occur inout int[in] "Give me the size and some starting data, and I'll play around with the data" Pass in (address, length); allow the contents to be modified in-place (current treatment of in int[], except that changing the length should be disallowed) out int[in] "Give me the size, and I'll give you the data" Pass in (address, length); initialise the array elements on entry; allow the contents to be modified in-place inout int[inout] "Give me an array, and I'll do what I like with it" Pass in reference to (address, length); anything goes (current treatment of inout int[]) out int[inout] "Give me a starting size, and I'll give you the data, changing the size if I want" Pass in reference to (address, length); initialise the array elements on entry; anything goes out int[out] "I'll give you an array" Pass in reference to (address, length), which is initialised to null Of course, the other combinations in[inout], in[out], inout[out] make little or no sense. I guess the extension to arrays of arrays would be straightforward, but I'm not sure. And combined with the existing system, while the syntax of my idea doesn't clash with it, it would cause confusion. And it would probalby clash if we tried to extend it to static array parameters. Maybe there's a better notation.... Stewart. -- My e-mail is valid but not my primary mailbox, aside from its being the unfortunate victim of intensive mail-bombing at the moment. Please keep replies on the 'group where everyone may benefit. | |||||||||||||||||||
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in/inout/out for arrays needs clear defining (Current message)
