Remove RevString and deprecate reverse(::AbstractString)

The `RevString` type for lazily reversed strings has been moved to the
LegacyStrings package. Fixes #22611.

Calling `reverse` on an `AbstractString` with no more specific method
has been deprecated in favor of explicitly converting to `String` before
reversing.

NEWS.md

@@ -100,6 +100,12 @@ Language changes
  * Prefix `&` for by-reference arguments to `ccall` has been deprecated in favor of
  `Ref` argument types ([#6080]).
 
+ * The `RevString` type for lazily reversed strings has been moved to the LegacyStrings
+ package ([#22611]).
+
+ * `reverse` on `AbstractString`s has been deprecated in favor of converting to `String`
+ before reversing ([#23612]).
+
 Breaking changes
 ----------------
 
@@ -1311,6 +1317,7 @@ Command-line option changes
 [#22532]: https://github.com/JuliaLang/julia/issues/22532
 [#22588]: https://github.com/JuliaLang/julia/issues/22588
 [#22605]: https://github.com/JuliaLang/julia/issues/22605
+[#22611]: https://github.com/JuliaLang/julia/issues/22611
 [#22666]: https://github.com/JuliaLang/julia/issues/22666
 [#22696]: https://github.com/JuliaLang/julia/issues/22696
 [#22703]: https://github.com/JuliaLang/julia/issues/22703
@@ -1340,3 +1347,4 @@ Command-line option changes
 [#23233]: https://github.com/JuliaLang/julia/issues/23233
 [#23342]: https://github.com/JuliaLang/julia/issues/23342
 [#23404]: https://github.com/JuliaLang/julia/issues/23404
+[#23612]: https://github.com/JuliaLang/julia/issues/23612

base/deprecated.jl

@@ -1855,6 +1855,12 @@ end
  nothing
 end
 
+# Issue #22611
+@deprecate_moved RevString "LegacyStrings"
+
+# PR 23612
+@deprecate reverse(s::AbstractString) reverse(String(s))
+
 # END 0.7 deprecations
 
 # BEGIN 1.0 deprecations

base/exports.jl

@@ -92,7 +92,6 @@ export
  Rational,
  Regex,
  RegexMatch,
- RevString,
  RoundFromZero,
  RoundDown,
  RoundingMode,

base/precompile.jl

@@ -581,9 +581,6 @@ precompile(Tuple{typeof(Base.LineEdit.complete_line), Base.LineEdit.PromptState,
 precompile(Tuple{typeof(Base.LineEdit.input_string_newlines_aftercursor), Base.LineEdit.PromptState})
 precompile(Tuple{typeof(Base.LineEdit.complete_line), Base.REPL.REPLCompletionProvider, Base.LineEdit.PromptState})
 precompile(Tuple{getfield(Base, Symbol("#kw##parse")), Array{Any, 1}, typeof(Base.parse), String})
-precompile(Tuple{typeof(Base.isvalid), Base.RevString{String}, Int64})
-precompile(Tuple{typeof(Base.nextind), Base.RevString{String}, Int64})
-precompile(Tuple{typeof(Base.search), Base.RevString{String}, Array{Char, 1}, Int64})
 precompile(Tuple{typeof(Base.rsearch), String, Array{Char, 1}, Int64})
 precompile(Tuple{getfield(Base.REPLCompletions, Symbol("#kw##find_start_brace")), Array{Any, 1}, typeof(Base.REPLCompletions.find_start_brace), String})
 precompile(Tuple{typeof(Core.Inference.isbits), Tuple{Void, Void, Void}})

base/repl/REPLCompletions.jl

@@ -225,13 +225,13 @@ end
 # closed start brace from the end of the string.
 function find_start_brace(s::AbstractString; c_start='(', c_end=')')
  braces = 0
- r = RevString(s)
- i = start(r)
+ i = endof(s)
  in_single_quotes = false
  in_double_quotes = false
  in_back_ticks = false
- while !done(r, i)
- c, i = next(r, i)
+ while i > 0
+ c = s[i]
+ nexti = prevind(s, i)
  if !in_single_quotes && !in_double_quotes && !in_back_ticks
  if c == c_start
  braces += 1
@@ -245,18 +245,19 @@ function find_start_brace(s::AbstractString; c_start='(', c_end=')')
  in_back_ticks = true
  end
  else
- if !in_back_ticks && !in_double_quotes && c == '\'' && !done(r, i) && next(r, i)[1]!='\\'
+ if !in_back_ticks && !in_double_quotes && c == '\'' && i > 0 && s[nexti] != '\\'
  in_single_quotes = !in_single_quotes
- elseif !in_back_ticks && !in_single_quotes && c == '"' && !done(r, i) && next(r, i)[1]!='\\'
+ elseif !in_back_ticks && !in_single_quotes && c == '"' && i > 0 && s[nexti] != '\\'
  in_double_quotes = !in_double_quotes
- elseif !in_single_quotes && !in_double_quotes && c == '`' && !done(r, i) && next(r, i)[1]!='\\'
+ elseif !in_single_quotes && !in_double_quotes && c == '`' && i > 0 && s[nexti] != '\\'
  in_back_ticks = !in_back_ticks
  end
  end
  braces == 1 && break
+ i = nexti
  end
  braces != 1 && return 0:-1, -1
- method_name_end = reverseind(r, i)
+ method_name_end = i - 1
  startind = nextind(s, rsearch(s, non_identifier_chars, method_name_end))
  return (startind:endof(s), method_name_end)
 end

base/shell.jl

@@ -12,21 +12,20 @@ function shell_parse(str::AbstractString, interpolate::Bool=true;
  special::AbstractString="")
  s = lstrip(str)
  # strips the end but respects the space when the string ends with "\\ "
- r = RevString(s)
- i = start(r)
- c_old = nothing
- while !done(r,i)
- c, j = next(r,i)
+ i = endof(s)
+ c_old = '\0' # initialized to a null byte for type stability
+ while i > 0
+ c = s[i]
  if c == '\\' && c_old == ' '
- i -= 1
+ i += 1
  break
  elseif !(c in _default_delims)
  break
  end
- i = j
+ i = prevind(s, i)
  c_old = c
  end
- s = s[1:end-i+1]
+ s = s[1:i]
 
  last_parse = 0:-1
  isempty(s) && return interpolate ? (Expr(:tuple,:()),last_parse) : ([],last_parse)

base/strings/search.jl

@@ -194,12 +194,6 @@ end
 search(s::AbstractString, t::AbstractString, i::Integer=start(s)) = _search(s, t, i)
 search(s::ByteArray, t::ByteArray, i::Integer=start(s)) = _search(s, t, i)
 
-function rsearch(s::AbstractString, c::Chars)
- j = search(RevString(s), c)
- j == 0 && return 0
- endof(s)-j+1
-end
-
 """
  rsearch(s::AbstractString, chars::Chars, [start::Integer])
 
@@ -212,44 +206,52 @@ julia> rsearch("aaabbb","b")
 6:6
 ```
 """
-function rsearch(s::AbstractString, c::Chars, i::Integer)
- e = endof(s)
- j = search(RevString(s), c, e-i+1)
- j == 0 && return 0
- e-j+1
+function rsearch(s::AbstractString, c::Chars, i::Integer=start(s))
+ @boundscheck checkbounds(s, i)
+ isempty(c) && return i
+ j = Int(i)
+ @inbounds while j > 0
+ s[j] in c && return j
+ j = prevind(s, j)
+ end
+ return 0
 end
 
 function _rsearchindex(s, t, i)
  if isempty(t)
- return 1 <= i <= nextind(s,endof(s)) ? i :
-  throw(BoundsError(s, i))
+ @boundscheck checkbounds(s, i)
+ return i
  end
- t = RevString(t)
- rs = RevString(s)
  l = endof(s)
- t1, j2 = next(t,start(t))
+ j2 = endof(t)
+ t1 = t[j2]
  while true
- i = rsearch(s,t1,i)
- if i == 0 return 0 end
- c, ii = next(rs,l-i+1)
- j = j2; k = ii
+ i = rsearch(s, t1, i)
+ i == 0 && return 0
+ c = s[i]
+ ii = prevind(s, i)
+ j, k = j2, ii
  matched = true
- while !done(t,j)
- if done(rs,k)
+ while j > 0
+ if k < 1
  matched = false
  break
  end
- c, k = next(rs,k)
- d, j = next(t,j)
+ # Using `reverseind` with `prevind` mimics `next` but for iteration over
+ # `reverse(s)` (without actually having to call `reverse`) since `reverseind`
+ # is the current index in `reverse(s)` and `prevind` is the index for the
+ # next iteration.
+ rs_k = reverseind(s, k)
+ c, k = s[rs_k], prevind(s, rs_k)
+ rt_j = reverseind(t, j)
+ d, j = t[rt_j], prevind(t, rt_j)
  if c != d
  matched = false
  break
  end
  end
- if matched
- return nextind(s,l-k+1)
- end
- i = l-ii+1
+ matched && return nextind(s, k)
+ i = ii
  end
 end
 

base/strings/types.jl

@@ -1,6 +1,6 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
-# SubString and RevString types
+# SubString type
 
 ## substrings reference original strings ##
 
@@ -97,35 +97,6 @@ function unsafe_convert(::Type{Ptr{R}}, s::SubString{String}) where R<:Union{Int
  convert(Ptr{R}, pointer(s.string)) + s.offset
 end
 
-## reversed strings without data movement ##
-
-struct RevString{T<:AbstractString} <: AbstractString
- string::T
-end
-
-endof(s::RevString) = endof(s.string)
-length(s::RevString) = length(s.string)
-sizeof(s::RevString) = sizeof(s.string)
-
-function next(s::RevString, i::Int)
- n = endof(s); j = n-i+1
- (s.string[j], n-prevind(s.string,j)+1)
-end
-
-"""
- reverse(s::AbstractString) -> AbstractString
-
-Reverses a string.
-
-# Examples
-```jldoctest
-julia> reverse("JuliaLang")
-"gnaLailuJ"
-```
-"""
-reverse(s::AbstractString) = RevString(s)
-reverse(s::RevString) = s.string
-
 ## reverse an index i so that reverse(s)[i] == s[reverseind(s,i)]
 
 """
@@ -148,7 +119,6 @@ Julia
 """
 reverseind(s::AbstractString, i) = chr2ind(s, length(s) + 1 - ind2chr(reverse(s), i))
 reverseind(s::Union{DirectIndexString,SubString{DirectIndexString}}, i::Integer) = length(s) + 1 - i
-reverseind(s::RevString, i::Integer) = endof(s) - i + 1
 reverseind(s::SubString{String}, i::Integer) =
  reverseind(s.string, nextind(s.string, endof(s.string))-s.offset-s.endof+i-1) - s.offset
 

base/strings/util.jl

@@ -173,14 +173,11 @@ julia> rstrip(a)
 ```
 """
 function rstrip(s::AbstractString, chars::Chars=_default_delims)
- r = RevString(s)
- i = start(r)
- while !done(r,i)
- c, j = next(r,i)
- if !(c in chars)
- return SubString(s, 1, endof(s)-i+1)
- end
- i = j
+ i = endof(s)
+ while i > 0
+ c = s[i]
+ c in chars || return SubString(s, 1, i)
+ i = prevind(s, i)
  end
  SubString(s, 1, 0)
 end

contrib/Julia_Notepad++.xml

@@ -25,7 +25,7 @@
  <Keywords name="Folders in comment, middle"></Keywords>
  <Keywords name="Folders in comment, close"></Keywords>
  <Keywords name="Keywords1">true false C_NULL Inf NaN Inf32 NaN32 nothing</Keywords>
- <Keywords name="Keywords2">AbstractArray AbstractMatrix AbstractRange AbstractRemoteRef AbstractSparseMatrix AbstractString AbstractVector Any ArgumentError Array Associative BigFloat BigInt BitArray BitMatrix BitVector Bool BunchKaufman Cchar Cdouble Cfloat Char CharString CholeskyDense CholeskyPivotedDense Cint Cintmax_t Clong Clonglong Colon Complex Complex128 Complex64 ComplexPair Cptrdiff_t Cshort Csize_t Cuchar Cuint Cuintmax_t Culong Culonglong Cushort DArray Dict Dims DisconnectException EOFError EachLine EnvHash ErrorException Exception Expr Factorization Filter Float Float32 Float64 Function GSVDDense IO IOBuffer IOStream ImaginaryUnit InsertionSort Int Int128 Int16 Int32 Int64 Int8 IntSet Integer KeyError LDLTTridiagonal LUDense LUTridiagonal LoadError LocalProcess Matrix MergeSort MethodError NTuple Number ObjectIdDict ObjectIdDict OrdinalRange ParseError PipeBuffer ProcessGroup Ptr QRDense QRPivotedDense QuickSort RangeIndex Rational Real Regex RegexMatch RegexMatchIterator RepString RevString Reverse SVDDense Set Signed SparseMatrixCSC SpawnNullStream Stat StridedArray StridedMatrix StridedVecOrMat StridedVector String SubArray SubDArray SubOrDArray SubString SymTridiagonal Symbol SystemError Task TCPSocket TimSort Tridiagonal Tuple Type TypeError UInt UInt128 UInt16 UInt32 UInt64 UInt8 UVError Union UnitRange Unsigned VecOrMat Vector VersionNumber Void WeakKeyDict WeakRef Zip</Keywords>
+ <Keywords name="Keywords2">AbstractArray AbstractMatrix AbstractRange AbstractRemoteRef AbstractSparseMatrix AbstractString AbstractVector Any ArgumentError Array Associative BigFloat BigInt BitArray BitMatrix BitVector Bool BunchKaufman Cchar Cdouble Cfloat Char CharString CholeskyDense CholeskyPivotedDense Cint Cintmax_t Clong Clonglong Colon Complex Complex128 Complex64 ComplexPair Cptrdiff_t Cshort Csize_t Cuchar Cuint Cuintmax_t Culong Culonglong Cushort DArray Dict Dims DisconnectException EOFError EachLine EnvHash ErrorException Exception Expr Factorization Filter Float Float32 Float64 Function GSVDDense IO IOBuffer IOStream ImaginaryUnit InsertionSort Int Int128 Int16 Int32 Int64 Int8 IntSet Integer KeyError LDLTTridiagonal LUDense LUTridiagonal LoadError LocalProcess Matrix MergeSort MethodError NTuple Number ObjectIdDict ObjectIdDict OrdinalRange ParseError PipeBuffer ProcessGroup Ptr QRDense QRPivotedDense QuickSort RangeIndex Rational Real Regex RegexMatch RegexMatchIterator RepString Reverse SVDDense Set Signed SparseMatrixCSC SpawnNullStream Stat StridedArray StridedMatrix StridedVecOrMat StridedVector String SubArray SubDArray SubOrDArray SubString SymTridiagonal Symbol SystemError Task TCPSocket TimSort Tridiagonal Tuple Type TypeError UInt UInt128 UInt16 UInt32 UInt64 UInt8 UVError Union UnitRange Unsigned VecOrMat Vector VersionNumber Void WeakKeyDict WeakRef Zip</Keywords>
  <Keywords name="Keywords3">abstract begin baremodule primitive break catch ccall const continue do else elseif end export finally for function global if struct import importall let local macro module quote return try mutable typealias using while</Keywords>
  <Keywords name="Keywords4">close enumerate error info open print println read write warn</Keywords>
  <Keywords name="Keywords5">print println</Keywords>

contrib/julia.xml

@@ -156,7 +156,6 @@
  <item> RegexMatch </item>
  <item> RegexMatchIterator </item>
  <item> RepString </item>
- <item> RevString </item>
  <item> Reverse </item>
  <item> Schur </item>
  <item> Set </item>

doc/src/manual/interacting-with-julia.md

@@ -67,7 +67,7 @@ When the cursor is at the beginning of the line, the prompt can be changed to a
 julia> ? # upon typing ?, the prompt changes (in place) to: help?>
 
 help?> string
-search: string String stringmime Cstring Cwstring RevString randstring bytestring SubString
+search: string String stringmime Cstring Cwstring randstring bytestring SubString
 
  string(xs...)
 

test/strings/types.jl

@@ -1,6 +1,6 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
-## SubString, RevString and Cstring tests ##
+## SubString and Cstring tests ##
 
 ## SubString tests ##
 u8str = "∀ ε > 0, ∃ δ > 0: |x-y| < δ ⇒ |f(x)-f(y)| < ε"
@@ -163,36 +163,24 @@ end
 
 ## Reverse strings ##
 
-let rs = RevString("foobar")
- @test length(rs) == 6
- @test sizeof(rs) == 6
- @test isascii(rs)
-end
-
-# issue #4586
-@test rsplit(RevString("ailuj"),'l') == ["ju","ia"]
-@test parse(Float64,RevString("64")) === 46.0
-
 # reverseind
 for T in (String, GenericString)
  for prefix in ("", "abcd", "\U0001d6a4\U0001d4c1", "\U0001d6a4\U0001d4c1c", " \U0001d6a4\U0001d4c1")
  for suffix in ("", "abcde", "\U0001d4c1β\U0001d6a4", "\U0001d4c1β\U0001d6a4c", " \U0001d4c1β\U0001d6a4")
  for c in ('X', 'δ', '\U0001d6a5')
- s = convert(T, string(prefix, c, suffix))
- r = reverse(s)
- ri = search(r, c)
- @test r == RevString(s)
- @test c == s[reverseind(s, ri)] == r[ri]
- s = RevString(s)
- r = reverse(s)
- ri = search(r, c)
- @test c == s[reverseind(s, ri)] == r[ri]
- s = convert(T, string(prefix, prefix, c, suffix, suffix))
- pre = convert(T, prefix)
- sb = SubString(s, nextind(pre, endof(pre)), endof(convert(T, string(prefix, prefix, c, suffix))))
- r = reverse(sb)
- ri = search(r, c)
- @test c == sb[reverseind(sb, ri)] == r[ri]
+ let s = convert(T, string(prefix, c, suffix))
+ r = reverse(String(s))
+ ri = search(r, c)
+ @test c == s[reverseind(s, ri)] == r[ri]
+ end
+ let s = convert(T, string(prefix, prefix, c, suffix, suffix))
+ pre = convert(T, prefix)
+ sb = SubString(s, nextind(pre, endof(pre)), endof(convert(T, string(prefix, prefix, c, suffix))))
+ r = reverse(String(sb))
+ ri = search(r, c)
+ sbs = String(sb)
+ @test c == sbs[reverseind(sbs, ri)] == r[ri]
+ end
  end
  end
  end