0000-interleave-iter

active/0000-interleave-iter.md

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+- Start Date: 2014-07-23
+- RFC PR #: (leave this empty)
+- Rust Issue #: (leave this empty)
+
+# Summary
+
+Adding an interleaving iterator to the set of core iterator adaptors. 
+That is `a_iter.interleave(b_iter)` `yields a1,b1,a2,b2,...` until one terminates.
+
+# Motivation
+
+There's no easy way to accomplish this with the current set of iterator adaptors, 
+and there are enough subtle corner cases that I wouldn't expect someone to
+trivially implement it correctly when they need it.
+
+Desirable for when something expects a single iterator, but you want to 
+interleave the contents of multiple iterators. For instance, if you wanted
+to create a stream of loosely unsorted data, you could do something like 
+`sorted.interleave(sorted.rev())`
+
+# Detailed design
+
+I've actually fully implemented this [in this pull request](https://github.com/rust-lang/rust/pull/15886),
+this is a retroactive RFC to see if this is desirable to have in libcore at all.
+
+# Drawbacks
+
+More code, more api. Otherwise only affects itself. Fully backcompat. 
+
+# Alternatives
+
+No real alternatives, it simply is or isn't available.
+
+# Unresolved questions
+
+It's possible to have interleave *not* terminate when any one of the source iterators terminates, 
+but rather just output the rest of the remaining iterator. This would increase complexity, and is not
+clearly desirable. In this vein, Interleave could potentially be augmented to provide all kinds of combinations of
+behaviour, such as offsetting the splicing of the iterators `(a1, a2, a3, b1, a4, b2, a5, b3, ...)` 
+or unbalanced usage of the sources `(a1, a2, b1, a3, a4, b2...)`.
+
+Would we want any of these?