Add back RopeString type for now

Author: ScottPJones

base/stringtypes.jl

@@ -1,6 +1,6 @@
 # This file is a part of Julia. License is MIT: http://julialang.org/license
 
-# SubString, RevString, and RepString types
+# SubString, RevString, RepString, and RopeString types
 
 ## substrings reference original strings ##
 
@@ -176,3 +176,49 @@ function repeat(s::ByteString, r::Integer)
 end
 
 (^)(s::AbstractString, r::Integer) = repeat(s,r)
+
+## ropes for efficient concatenation, etc. ##
+
+immutable RopeString <: AbstractString
+    head::AbstractString
+    tail::AbstractString
+    depth::Int32
+    endof::Int
+
+    RopeString(h::RopeString, t::RopeString) =
+        strdepth(h.tail) + strdepth(t) < strdepth(h.head) ?
+            RopeString(h.head, RopeString(h.tail, t)) :
+            new(h, t, max(h.depth,t.depth)+1, endof(h)+endof(t))
+
+    RopeString(h::RopeString, t::AbstractString) =
+        strdepth(h.tail) < strdepth(h.head) ?
+            RopeString(h.head, RopeString(h.tail, t)) :
+            new(h, t, h.depth+1, endof(h)+endof(t))
+
+    RopeString(h::AbstractString, t::RopeString) =
+        strdepth(t.head) < strdepth(t.tail) ?
+            RopeString(RopeString(h, t.head), t.tail) :
+            new(h, t, t.depth+1, endof(h)+endof(t))
+
+    RopeString(h::AbstractString, t::AbstractString) =
+        new(h, t, 1, endof(h)+endof(t))
+end
+RopeString(s::AbstractString) = RopeString(s,"")
+
+strdepth(s::AbstractString) = 0
+strdepth(s::RopeString) = s.depth
+
+function next(s::RopeString, i::Int)
+    eh = endof(s.head)
+    if i <= eh
+        return next(s.head, i)
+    else
+        c, j = next(s.tail, i-eh)
+        return c, j+eh
+    end
+end
+
+endof(s::RopeString) = s.endof
+length(s::RopeString) = length(s.head) + length(s.tail)
+write(io::IO, s::RopeString) = (write(io, s.head); write(io, s.tail))
+sizeof(s::RopeString) = sizeof(s.head) + sizeof(s.tail)

test/stringtypes.jl

@@ -190,3 +190,7 @@ let
     @test srep[7] == 'β'
     @test_throws BoundsError srep[8]
 end
+
+## Rope strings ##
+
+@test sizeof(RopeString("abc","def")) == 6