Add a draft for rename_connect_to_join

text/0000-rename-connect-to-join.md

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+- Feature Name: `rename_connect_to_join`
+- Start Date: 2015-05-02
+- RFC PR: (leave this empty)
+- Rust Issue: (leave this empty)
+
+# Summary
+
+Rename `.connect()` to `.join()` in `SliceConcatExt`.
+
+# Motivation
+
+Rust has a string concatenation method named `.connect()` in `SliceConcatExt`.
+However, this does not align with the precedents in other languages. Most
+languages use `.join()` for that purpose, as seen later.
+
+This is probably because, in the ancient Rust, `join` was a keyword to join a
+task. However, `join` retired as a keyword in 2011 with the commit
+rust-lang/rust@d1857d3. While `.connect()` is technically correct, the name may
+not be directly inferred by the users of the mainstream languages. There was [a
+question] about this on reddit.
+
+[a question]: http://www.reddit.com/r/rust/comments/336rj3/whats_the_best_way_to_join_strings_with_a_space/
+
+The languages that use the name of `join` are:
+
+- Python: [str.join](https://docs.python.org/3/library/stdtypes.html#str.join)
+- Ruby: [Array.join](http://ruby-doc.org/core-2.2.0/Array.html#method-i-join)
+- JavaScript: [Array.prototype.join](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join)
+- Go: [strings.Join](https://golang.org/pkg/strings/#Join)
+- C#: [String.Join](https://msdn.microsoft.com/en-us/library/dd783876%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396)
+- Java: [String.join](http://docs.oracle.com/javase/8/docs/api/java/lang/String.html#join-java.lang.CharSequence-java.lang.Iterable-)
+- Perl: [join](http://perldoc.perl.org/functions/join.html)
+
+The languages not using `join` are as follows. Interestingly, they are
+all functional-ish languages.
+
+- Haskell: [intercalate](http://hackage.haskell.org/package/text-1.2.0.4/docs/Data-Text.html#v:intercalate)
+- OCaml: [String.concat](http://caml.inria.fr/pub/docs/manual-ocaml/libref/String.html#VALconcat)
+- F#: [String.concat](https://msdn.microsoft.com/en-us/library/ee353761.aspx)
+
+Note that Rust also has `.concat()` in `SliceConcatExt`, which is a specialized
+version of `.connect()` that uses an empty string as a separator.
+
+# Detailed design
+
+While the `SliceConcatExt` trait is unstable, the `.connect()` method itself is
+marked as stable. So we need to:
+
+1. Deprecate the `.connect()` method.
+2. Add the `.join()` method.
+
+Or, if we are to achieve the [instability guarantee], we may remove the old
+method entirely, as it's still pre-1.0. However, the author considers that this
+may require even more consensus.
+
+[instability guarantee]: https://github.com/rust-lang/rust/issues/24928
+
+# Drawbacks
+
+Having a deprecated method in a newborn language is not pretty.
+
+If we do remove the `.connect()` method, the language becomes pretty again, but
+it breaks the stability guarantee at the same time.
+
+# Alternatives
+
+Keep the status quo. Improving searchability in the docs will help newcomers
+find the appropriate method.
+
+# Unresolved questions
+
+Are there even more clever names for the method? How about `.homura()`, or
+`.madoka()`?