On 3/30/11 4:06 PM, spir wrote:
Hello,I was trying std.container's SList and noticed foreach iteration works for it, while it defines neither opApply, nore a (complete) input range interface. But it does implement a parameter-less opSlice, which maps to "l2 = l1[];". More precisely, SList (as other container types) defines a 'Range' struct type which is the return type of opSlice(). TDPL states this method should automagically deal as standard traversal for foreach (when no opApply or range interface is defined on the collection to be traverseditself, I guess). But the magic did not work up to very recently. Does this mean this feature is now implemented? (Note: I tried it for a custom collection type, and it worked fine.) If yes, I guess it deserves an announce on the mailing list, as many of thus were waiting for it (hurray!). And a clear explanation at three places: * in the 'foreach' section of the language reference manual * in std.range's doc * in std.container's doc Note that this feature fills a long-standing gap in the unification of collections & ranges: there have been until now 2 contradictory requirements upon ranges: 1. A collection should be iterable (indeed). 2. A collection should /not/ implement a range interface (be its own range), instead it should provide one or more methods returning traversal ranges. This is supposed to be more flexible. The only solutions were either to provide opApply in addition to 2., or to force the user explicitely calling the methods, as in: foreach (element; myCollection.elements()) {...} Both are unsatisfying for different reasons. Thank to the "total slice" magic, opSlice() now implicitely deals as /standard/ traversal for a collection. Like if it were a kind of 'opTraversal'. This is exactly equivalent, I guess, to Python's __iter__. opSlice() is thus, if I understand correctly, supposed to return a 'traversable' thingy, typically an input range. I have not yet tried to provide a collection implementing opSlice() to funcs expecting a range. Hope this works as expected, or it will do so soon. [See also thread about "multiple-item traversal ranges"] Denis
Do we have three ways now to implement iteration, opApply, opSlice and ranges?
-- /Jacob Carlborg
