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.

Author: ararslan

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
 ----------------
 
@@ -1315,6 +1321,7 @@ 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
@@ -1344,3 +1351,4 @@ 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 ##
 
@@ -97,47 +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.
-
-Technically, this function reverses the codepoints in a string, and its
-main utility is for reversed-order string processing, especially for reversed
-regular-expression searches.  See also [`reverseind`](@ref) to convert indices
-in `s` to indices in `reverse(s)` and vice-versa, and [`graphemes`](@ref)
-to operate on user-visible "characters" (graphemes) rather than codepoints.
-
-# Examples
-```jldoctest
-julia> reverse("JuliaLang")
-"gnaLailuJ"
-
-julia> reverse("ax̂e") # combining characters can lead to surprising results
-"êxa"
-
-julia> join(reverse(collect(graphemes("ax̂e")))) # reverses graphemes
-"ex̂a"
-```
-"""
-reverse(s::AbstractString) = RevString(s)
-reverse(s::RevString) = s.string
-
 ## reverse an index i so that reverse(s)[i] == s[reverseind(s,i)]
 
 """
@@ -160,7 +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...)
 

doc/src/stdlib/strings.md

@@ -37,7 +37,7 @@ Base.rsearch
 Base.searchindex
 Base.rsearchindex
 Base.contains(::AbstractString, ::AbstractString)
-Base.reverse(::AbstractString)
+Base.reverse(::String)
 Base.replace
 Base.split
 Base.rsplit

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