Add RevString from Base

src/LegacyStrings.jl

@@ -9,6 +9,7 @@ export
     ByteString,
     ASCIIString,
     RepString,
+    RevString,
     UTF8String,
     UTF16String,
     UTF32String,
@@ -104,4 +105,10 @@ using Compat
     else
         include("rep.jl")
     end
+
+    if isdefined(Base, :RevString)
+        using Base: RevString
+    else
+        include("rev.jl")
+    end
 end # module

src/rev.jl

@@ -0,0 +1,19 @@
+# This file includes code that was formerly a part of Julia. License is MIT: https://julialang.org/license
+
+## reversed strings without data movement ##
+
+immutable 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::RevString) = s.string
+reverseind(s::RevString, i::Integer) = endof(s) - i + 1

test/runtests.jl

@@ -550,3 +550,31 @@ let
     @test srep[7] == 'β'
     @test_throws BoundsError srep[8]
 end
+
+
+## Reverse strings ##
+
+let
+    rs = RevString("foobar")
+    @test length(rs) == 6
+    @test sizeof(rs) == 6
+    @test isascii(rs)
+
+    # Base issue #4586
+    @test rsplit(RevString("ailuj"),'l') == ["ju","ia"]
+    @test parse(Float64,RevString("64")) === 46.0
+
+    # reverseind
+    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(String, string(prefix, c, suffix))
+                rs = RevString(s)
+                r = reverse(s)
+                @test r == rs
+                ri = search(r, c)
+                @test c == s[reverseind(s, ri)] == r[ri]
+            end
+        end
+    end
+end