Remove str::{windows,chunks} and <[T]>::subslice_offset

Author: ftxqxd

text/0000-slice-string-symmetry.md

@@ -5,63 +5,64 @@
 
 # Summary
 
-Add some methods that already exist on slices to strings and vice versa.
-Specifically, the following methods should be added:
+Add some methods that already exist on slices to strings. Specifically, the
+following methods should be added:
 
-- `str::chunks`
-- `str::windows`
 - `str::into_string`
-- `String::into_boxed_slice`
-- `<[T]>::subslice_offset`
+- `String::into_boxed_str`
 
 # Motivation
 
 Conceptually, strings and slices are similar types. Many methods are already
 shared between the two types due to their similarity. However, not all methods
 are shared between the types, even though many could be. This is a little
 unexpected and inconsistent. Because of that, this RFC proposes to remedy this
-by adding a few methods to both strings and slices to even out these two types’
-available methods.
+by adding a few methods to strings to even out these two types’ available
+methods.
 
-# Detailed design
-
-Add the following methods to `str`, presumably as inherent methods:
+Specifically, it is currently very difficult to construct a `Box<str>`, while it
+is fairly simple to make a `Box<[T]>` by using `Vec::into_boxed_slice`. This RFC
+proposes a means of creating a `Box<str>` by converting a `String`.
 
-- `chunks(&self, n: usize) -> Chunks`: Returns an iterator that yields the
-  *characters* (not bytes) of the string in groups of `n` at a time. Iterator
-  element type: `&str`.
+# Detailed design
 
-- `windows(&self, n: usize) -> Windows`: Returns an iterator over all contiguous
-  windows of character length `n`. Iterator element type: `&str`.
+Add the following method to `str`, presumably as an inherent method:
 
 - `into_string(self: Box<str>) -> String`: Returns `self` as a `String`. This is
   equivalent to `[T]`’s `into_vec`.
 
-`split_at(&self, mid: usize) -> (&str, &str)` would also be on this list, but
-there is [an existing RFC](https://github.com/rust-lang/rfcs/pull/1123) for it.
-
 Add the following method to `String` as an inherent method:
 
-- `into_boxed_slice(self) -> Box<str>`: Returns `self` as a `Box<str>`,
+- `into_boxed_str(self) -> Box<str>`: Returns `self` as a `Box<str>`,
   reallocating to cut off any excess capacity if needed. This is required to
-  provide a safe means of creating `Box<str>`.
-
-Add the following method to `[T]` (for all `T`), presumably as an inherent
-method:
+  provide a safe means of creating `Box<str>`. This is equivalent to `Vec<T>`’s
+  `into_boxed_slice`.
 
-- `subslice_offset(&self, inner: &[T]) -> usize`: Returns the offset (in
-  elements) of an inner slice relative to an outer slice. Panics of `inner` is
-  not contained within `self`.
 
 # Drawbacks
 
-- `str::subslice_offset` is already unstable, so creating a similar method on
-  `[T]` is perhaps not such a good idea.
+None, yet.
 
 # Alternatives
 
-- Do a subset of the proposal. For example, the `Box<str>`-related methods could
-  be removed.
+- The original version of this RFC had a few extra methods:
+  - `str::chunks(&self, n: usize) -> Chunks`: Returns an iterator that yields
+    the *characters* (not bytes) of the string in groups of `n` at a time.
+    Iterator element type: `&str`.
+
+  - `str::windows(&self, n: usize) -> Windows`: Returns an iterator over all
+    contiguous windows of character length `n`. Iterator element type: `&str`.
+
+    This and `str::chunks` aren’t really useful without proper treatment of
+    graphemes, so they were removed from the RFC.
+
+  - `<[T]>::subslice_offset(&self, inner: &[T]) -> usize`: Returns the offset
+    (in elements) of an inner slice relative to an outer slice. Panics of
+    `inner` is not contained within `self`.
+
+    `str::subslice_offset` isn’t yet stable and its usefulness is dubious, so
+    this method was removed from the RFC.
+
 
 # Unresolved questions