RFC: deprecate * in favor of new ++ concatenation operator

base/abstractarray.jl

@@ -1299,6 +1299,19 @@ julia> hcat(c...)
 """
 hcat(X...) = cat(Val{2}, X...)
 
+"""
+    ++(X...)
+
+`++` is a generic concatenation operator.  By default, it
+calls [`vcat`](@ref), concatenating arrays and elements thereof.
+For strings and characters, it performs string concatenation.
+Similarly, for other types it may perform an appropriate concatenation
+operation.
+"""
+++(X...) = concat(concat_typeof(X...), X...)
+concat(::Type{<:Any}, X...) = vcat(X...) # default
+concat_rule(::Type{<:AbstractArray}, S) = (@_inline_meta; Array) # arrays should concatenate to arrays
+
 typed_vcat(T::Type, X...) = cat_t(Val{1}, T, X...)
 typed_hcat(T::Type, X...) = cat_t(Val{2}, T, X...)
 

base/abstractarraymath.jl

@@ -387,7 +387,7 @@ _rshps(shp, shp_i, sz, ::Tuple{}, o) =
     (n = length(shp); N = n + length(sz); _reperr("inner", n, N))
 _rshps(shp, shp_i, sz, i, ::Tuple{}) =
     (n = length(shp); N = n + length(sz); _reperr("outer", n, N))
-_reperr(s, n, N) = throw(ArgumentError("number of " * s * " repetitions " *
+_reperr(s, n, N) = throw(ArgumentError("number of " ++ s ++ " repetitions " ++
     "($n) cannot be less than number of dimensions of input ($N)"))
 
 @propagate_inbounds function _repeat(A::AbstractArray, inner, outer)

base/atomics.jl

@@ -421,7 +421,7 @@ for typ in atomictypes
         fn = Symbol("atomic_", rmw, "!")
         if (rmw == "max" || rmw == "min") && typ <: Unsigned
             # LLVM distinguishes signedness in the operation, not the integer type.
-            rmw = "u" * rmw
+            rmw = "u" ++ rmw
         end
         if typ <: Integer
             @eval $fn(x::Atomic{$typ}, v::$typ) =

base/broadcast.jl

@@ -420,7 +420,7 @@ julia> string.(("one","two","three","four"), ": ", 1:4)
  "three: 3"
  "four: 4"
 
-julia> Nullable("X") .* "Y"
+julia> Nullable("X") .++ "Y"
 Nullable{String}("XY")
 
 julia> broadcast(/, 1.0, Nullable(2.0))

base/client.jl

@@ -219,7 +219,7 @@ parse_input_line(s::AbstractString) = parse_input_line(String(s))
 function parse_input_line(io::IO)
     s = ""
     while !eof(io)
-        s *= readline(io, chomp=false)
+        s = s ++ readline(io, chomp=false)
         e = parse_input_line(s)
         if !(isa(e,Expr) && e.head === :incomplete)
             return e

base/dates/periods.jl

@@ -10,7 +10,7 @@ for period in (:Year, :Month, :Week, :Day, :Hour, :Minute, :Second, :Millisecond
     period_str = string(period)
     accessor_str = lowercase(period_str)
     # Convenience method for show()
-    @eval _units(x::$period) = " " * $accessor_str * (abs(value(x)) == 1 ? "" : "s")
+    @eval _units(x::$period) = " " ++ $accessor_str ++ (abs(value(x)) == 1 ? "" : "s")
     # periodisless
     @eval periodisless(x::$period, y::$period) = value(x) < value(y)
     # AbstractString parsing (mainly for IO code)
@@ -334,7 +334,7 @@ function Base.string(x::CompoundPeriod)
     else
         s = ""
         for p in x.periods
-            s *= ", " * string(p)
+            s = string(s, ", ", p)
         end
         return s[3:end]
     end

base/deprecated.jl

@@ -395,8 +395,8 @@ export $
 
 # promote_op method where the operator is also a type
 function promote_op(op::Type, Ts::Type...)
-    depwarn("promote_op(op::Type, ::Type...) is deprecated as it is no " *
-            "longer needed in Base. If you need its functionality, consider " *
+    depwarn("promote_op(op::Type, ::Type...) is deprecated as it is no " ++
+            "longer needed in Base. If you need its functionality, consider " ++
             "defining it locally.", :promote_op)
     if isdefined(Core, :Inference)
         return Core.Inference.return_type(op, Tuple{Ts...})
@@ -721,8 +721,8 @@ _promote_array_type(::typeof(\), ::Type{<:Integer}, ::Type{Bool}, T::Type) = T
 _promote_array_type(F, ::Type{<:Integer}, ::Type{Bool}, T::Type) = T
 _promote_array_type{T<:AbstractFloat}(F, ::Type{<:Union{Complex, Real}}, ::Type{Complex{T}}, ::Type) = Complex{T}
 function promote_array_type(F, R, S, T)
-    Base.depwarn("`promote_array_type` is deprecated as it is no longer needed " *
-                 "in Base. See https://github.com/JuliaLang/julia/issues/19669 " *
+    Base.depwarn("`promote_array_type` is deprecated as it is no longer needed " ++
+                 "in Base. See https://github.com/JuliaLang/julia/issues/19669 " ++
                  "for more information.", :promote_array_type)
     _promote_array_type(F, R, S, T)
 end
@@ -1165,8 +1165,8 @@ end
         return func
     else
         msg = "$f($sig; negate=$negate) is deprecated, use $f("
-        negate && (msg *= "!")
-        msg *= "$sig) instead."
+        negate && (msg = msg ++ "!")
+        msg = msg ++ "$sig) instead."
         Base.depwarn(msg, f)
         return negate ? !func : func
     end
@@ -1434,6 +1434,10 @@ module Operators
 end
 export Operators
 
+# deprecate old string-concatenation ops in favor of ++
+@deprecate (*)(s1::AbstractString, ss::AbstractString...) (++)(s1, ss...)
+@deprecate (^)(s::AbstractString, r::Integer) repeat(s,r)
+
 # PR #21956
 # This mimics the structure as it was defined in Base to avoid directly breaking code
 # that assumes this structure

base/distributed/cluster.jl

@@ -112,7 +112,7 @@ function check_worker_state(w::Worker)
             wait(w.c_state)
             w.state == W_CREATED && error("peer $(w.id) didn't connect to $(myid()) within $timeout seconds")
         else
-            error("peer $(w.id) is not connected to $(myid()). Topology : " * string(PGRP.topology))
+            error("peer $(w.id) is not connected to $(myid()). Topology : ", PGRP.topology)
         end
     end
 end

base/exports.jl

@@ -236,6 +236,7 @@ export
     :,
     =>,
     ∘,
+    ++,
     A_ldiv_B!,
     A_ldiv_Bc,
     A_ldiv_Bt,

base/interactiveutil.jl

@@ -222,7 +222,7 @@ function _show_cpuinfo(io::IO, info::Sys.CPUinfo, header::Bool=true, prefix::Abs
     tck = Sys.SC_CLK_TCK
     if header
         println(io, info.model, ": ")
-        print(io, " "^length(prefix))
+        print(io, repeat(" ",length(prefix)))
         if tck > 0
             @printf(io, "    %5s    %9s    %9s    %9s    %9s    %9s\n",
                     "speed", "user", "nice", "sys", "idle", "irq")
@@ -419,8 +419,8 @@ function gen_call_with_extracted_types(__module__, fcn, ex0)
     end
     if (!is_macro && ex.head == :thunk) || exret.head == :none
         exret = Expr(:call, :error, "expression is not a function call, "
-                                  * "or is too complex for @$fcn to analyze; "
-                                  * "break it down to simpler parts if possible")
+                                  ++ "or is too complex for @$fcn to analyze; "
+                                  ++ "break it down to simpler parts if possible")
     end
     exret
 end
@@ -690,7 +690,7 @@ function runtests(tests = ["all"], numcores = ceil(Int, Sys.CPU_CORES / 2))
     catch
         buf = PipeBuffer()
         versioninfo(buf)
-        error("A test has failed. Please submit a bug report (https://github.com/JuliaLang/julia/issues)\n" *
+        error("A test has failed. Please submit a bug report (https://github.com/JuliaLang/julia/issues)\n" ++
               "including error messages above and the output of versioninfo():\n$(readstring(buf))")
     end
 end

base/libgit2/callbacks.jl

@@ -205,7 +205,7 @@ function credentials_callback(libgit2credptr::Ptr{Ptr{Void}}, url_ptr::Cstring,
 
     # parse url for schema and host
     urlparts = match(URL_REGEX, url)
-    schema = urlparts[:scheme] === nothing ? "" : urlparts[:scheme] * "://"
+    schema = urlparts[:scheme] === nothing ? "" : urlparts[:scheme] ++ "://"
     urlusername = urlparts[:user] === nothing ? "" : urlparts[:user]
     host = urlparts[:host]
 
@@ -241,7 +241,7 @@ function credentials_callback(libgit2credptr::Ptr{Ptr{Void}}, url_ptr::Cstring,
     # with the remote host.
     if err == 0
         if explicit
-            warn("The explicitly provided credentials were incompatible with " *
+            warn("The explicitly provided credentials were incompatible with ",
                  "the server's supported authentication methods")
         end
         err = Cint(Error.EAUTH)

base/libgit2/utils.jl

@@ -35,7 +35,7 @@ function prompt(msg::AbstractString; default::AbstractString="", password::Bool=
     if is_windows() && password
         error("Command line prompt not supported for password entry on windows. Use winprompt instead")
     end
-    msg = !isempty(default) ? msg*" [$default]:" : msg*":"
+    msg = !isempty(default) ? msg++" [$default]:" : msg++":"
     uinput = if password
         Base.getpass(msg)
     else

base/libuv.jl

@@ -66,7 +66,7 @@ uverrorname(err::UVError) = uverrorname(err.code)
 
 uv_error(prefix::Symbol, c::Integer) = uv_error(string(prefix),c)
 uv_error(prefix::AbstractString, c::Integer) = c < 0 ? throw(UVError(prefix,c)) : nothing
-show(io::IO, e::UVError) = print(io, e.prefix*": "*struverror(e)*" ("*uverrorname(e)*")")
+show(io::IO, e::UVError) = print(io, e.prefix,": ",struverror(e)," (",uverrorname(e),")")
 
 ## event loop ##
 

base/linalg/cholesky.jl

@@ -126,8 +126,8 @@ end
 
 chol!(x::Number, uplo) = ((C, info) = _chol!(x, uplo); @assertposdef C info)
 
-non_hermitian_error(f) = throw(ArgumentError("matrix is not symmetric/" *
-    "Hermitian. This error can be avoided by calling $f(Hermitian(A)) " *
+non_hermitian_error(f) = throw(ArgumentError("matrix is not symmetric/" ++
+    "Hermitian. This error can be avoided by calling $f(Hermitian(A)) " ++
     "which will ignore either the upper or lower triangle of the matrix."))
 
 # chol!. Destructive methods for computing Cholesky factor of real symmetric or Hermitian

base/linalg/generic.jl

@@ -1058,7 +1058,7 @@ function linreg(x::AbstractVector, y::AbstractVector)
     # b = cov(X, Y)/var(X)
     # a = mean(Y) - b*mean(X)
     if size(x) != size(y)
-        throw(DimensionMismatch("x has size $(size(x)) and y has size $(size(y)), " *
+        throw(DimensionMismatch("x has size $(size(x)) and y has size $(size(y)), " ++
             "but these must be the same size"))
     end
     mx = mean(x)

base/linalg/triangular.jl

@@ -130,7 +130,7 @@ getindex(A::UpperTriangular, i::Integer, j::Integer) =
 
 function setindex!(A::UpperTriangular, x, i::Integer, j::Integer)
     if i > j
-        x == 0 || throw(ArgumentError("cannot set index in the lower triangular part " *
+        x == 0 || throw(ArgumentError("cannot set index in the lower triangular part " ++
             "($i, $j) of an UpperTriangular matrix to a nonzero value ($x)"))
     else
         A.data[i,j] = x
@@ -140,10 +140,10 @@ end
 
 function setindex!(A::UnitUpperTriangular, x, i::Integer, j::Integer)
     if i > j
-        x == 0 || throw(ArgumentError("cannot set index in the lower triangular part " *
+        x == 0 || throw(ArgumentError("cannot set index in the lower triangular part " ++
             "($i, $j) of a UnitUpperTriangular matrix to a nonzero value ($x)"))
     elseif i == j
-        x == 1 || throw(ArgumentError("cannot set index on the diagonal ($i, $j) " *
+        x == 1 || throw(ArgumentError("cannot set index on the diagonal ($i, $j) " ++
             "of a UnitUpperTriangular matrix to a non-unit value ($x)"))
     else
         A.data[i,j] = x
@@ -153,7 +153,7 @@ end
 
 function setindex!(A::LowerTriangular, x, i::Integer, j::Integer)
     if i < j
-        x == 0 || throw(ArgumentError("cannot set index in the upper triangular part " *
+        x == 0 || throw(ArgumentError("cannot set index in the upper triangular part " ++
             "($i, $j) of a LowerTriangular matrix to a nonzero value ($x)"))
     else
         A.data[i,j] = x
@@ -163,10 +163,10 @@ end
 
 function setindex!(A::UnitLowerTriangular, x, i::Integer, j::Integer)
     if i < j
-        x == 0 || throw(ArgumentError("cannot set index in the upper triangular part " *
+        x == 0 || throw(ArgumentError("cannot set index in the upper triangular part " ++
             "($i, $j) of a UnitLowerTriangular matrix to a nonzero value ($x)"))
     elseif i == j
-        x == 1 || throw(ArgumentError("cannot set index on the diagonal ($i, $j) " *
+        x == 1 || throw(ArgumentError("cannot set index on the diagonal ($i, $j) " ++
             "of a UnitLowerTriangular matrix to a non-unit value ($x)"))
     else
         A.data[i,j] = x

base/loading.jl

@@ -140,7 +140,7 @@ function find_all_in_cache_path(mod::Symbol)
     name = string(mod)
     paths = String[]
     for prefix in LOAD_CACHE_PATH
-        path = joinpath(prefix, name*".ji")
+        path = joinpath(prefix, name++".ji")
         if isfile_casesensitive(path)
             push!(paths, path)
         end
@@ -345,7 +345,7 @@ function require_modname(name::AbstractString)
         if endswith(name, ".jl")
             tmp = name[1:end-3]
             for prefix in LOAD_CACHE_PATH
-                path = joinpath(prefix, tmp*".ji")
+                path = joinpath(prefix, tmp++".ji")
                 if isfile(path)
                     return tmp
                 end
@@ -658,7 +658,7 @@ function compilecache(name::String)
     if !isdir(cachepath)
         mkpath(cachepath)
     end
-    cachefile::String = abspath(cachepath, name*".ji")
+    cachefile::String = abspath(cachepath, name++".ji")
     # build up the list of modules that we want the precompile process to preserve
     concrete_deps = copy(_concrete_dependencies)
     for existing in names(Main)

base/markdown/Common/block.jl

@@ -303,7 +303,7 @@ function list(stream::IO, block::MD)
                 end
             else
                 newline = false
-                if startswith(stream, " "^indent)
+                if startswith(stream, repeat(" ",indent))
                     # Indented text that is part of the current list item.
                     print(buffer, readline(stream, chomp=false))
                 else

base/markdown/GitHub/GitHub.jl

@@ -16,9 +16,10 @@ function fencedcode(stream::IO, block::MD)
         ch in flavor && return false
 
         buffer = IOBuffer()
+        chn = repeat(string(ch),n)
         while !eof(stream)
             line_start = position(stream)
-            if startswith(stream, string(ch) ^ n)
+            if startswith(stream, chn)
                 if !startswith(stream, string(ch))
                     if flavor == "math"
                         push!(block, LaTeX(String(take!(buffer)) |> chomp))
@@ -63,4 +64,3 @@ end
 
                 linebreak, escapes, en_dash, inline_code, asterisk_bold,
                 asterisk_italic, image, footnote_link, link, autolink]
-

base/markdown/GitHub/table.jl

@@ -91,15 +91,15 @@ function padcells!(rows, align; len = length, min = 0)
     for i = 1:length(rows), j = indices(rows[1],1)
         cell = rows[i][j]
         lpad, rpad = padding(len(cell), widths[j], align[j])
-        rows[i][j] = " "^lpad * cell * " "^rpad
+        rows[i][j] = repeat(" ",lpad) ++ cell ++ repeat(" ",rpad)
     end
     return rows
 end
 
 _dash(width, align) =
-    align == :l ? ":" * "-"^width * " " :
-    align == :r ? " " * "-"^width * ":" :
-    align == :c ? ":" * "-"^width * ":" :
+    align == :l ? ":" ++ repeat("-",width) ++ " " :
+    align == :r ? " " ++ repeat("-",width) ++ ":" :
+    align == :c ? ":" ++ repeat("-",width) ++ ":" :
     throw(ArgumentError("Invalid alignment $align"))
 
 function plain(io::IO, md::Table)

base/markdown/parse/util.jl

@@ -179,20 +179,21 @@ function parse_inline_wrapper(stream::IO, delimiter::AbstractString; rep = false
             (read(stream, Char) in delimiter) && return nothing
         end
         n = nmin
-        startswith(stream, delimiter^n) || return nothing
+        startswith(stream, repeat(delimiter,n)) || return nothing
         while startswith(stream, delimiter); n += 1; end
         !rep && n > nmin && return nothing
         !eof(stream) && Char(peek(stream)) in whitespace && return nothing
 
         buffer = IOBuffer()
+        delimitern = repeat(delimiter,n)
         while !eof(stream)
             char = read(stream, Char)
             write(buffer, char)
-            if !(char in whitespace || char == '\n' || char in delimiter) && startswith(stream, delimiter^n)
+            if !(char in whitespace || char == '\n' || char in delimiter) && startswith(stream, delimitern)
                 trailing = 0
                 while startswith(stream, delimiter); trailing += 1; end
                 trailing == 0 && return String(take!(buffer))
-                write(buffer, delimiter ^ (n + trailing))
+                write(buffer, repeat(delimiter, n + trailing))
             end
         end
     end

base/markdown/render/latex.jl

@@ -25,7 +25,7 @@ function latex(io::IO, content::Vector)
 end
 
 function latex(io::IO, header::Header{l}) where l
-    tag = l < 4 ? "sub"^(l-1) * "section" : "sub"^(l-4) * "paragraph"
+    tag = l < 4 ? repeat("sub",l-1) ++ "section" : repeat("sub",l-4) ++ "paragraph"
     wrapinline(io, tag) do
         latexinline(io, header.text)
     end

base/markdown/render/plain.jl

@@ -14,7 +14,7 @@ end
 plain(io::IO, md::MD) = plain(io, md.content)
 
 function plain(io::IO, header::Header{l}) where l
-    print(io, "#"^l*" ")
+    print(io, repeat("#",l)++" ")
     plaininline(io, header.text)
     println(io)
 end
@@ -122,7 +122,7 @@ plaininline(io::IO, md::Italic) = plaininline(io, "*", md.text, "*")
 function plaininline(io::IO, md::Code)
     if contains(md.code, "`")
         n = maximum(length(m) for m in matchall(r"(`+)", md.code))
-        s = "`"^((iseven(n) ? 1 : 2) + n)
+        s = repeat("`", (iseven(n) ? 1 : 2) + n)
         print(io, s, Base.startswith(md.code, "`") ? " " : "")
         print(io, md.code, endswith(md.code, "`") ? " " : "", s)
     else

base/markdown/render/rst.jl

@@ -42,7 +42,7 @@ function rst(io::IO, list::List)
         print(io, bullet)
         lines = split(rstrip(sprint(rst, item)), '\n')
         for (n, line) in enumerate(lines)
-            print(io, (n == 1 || isempty(line)) ? "" : " "^length(bullet), line)
+            print(io, (n == 1 || isempty(line)) ? "" : repeat(" ",length(bullet)), line)
             n < length(lines) && println(io)
         end
         println(io)