add replace(io, str, patterns...)

NEWS.md

@@ -33,6 +33,8 @@ New library features
 * The `initialized=true` keyword assignment for `sortperm!` and `partialsortperm!`
   is now a no-op ([#47979]). It previously exposed unsafe behavior ([#47977]).
 * `binomial(x, k)` now supports non-integer `x` ([#48124]).
+* `replace(string, pattern...)` now supports an optional `IO` argument to
+  write the output to a stream rather than returning a string ([#48625]).
 * A `CartesianIndex` is now treated as a "scalar" for broadcasting ([#47044]).
 
 Standard library changes

base/strings/util.jl

@@ -681,8 +681,8 @@ _free_pat_replacer(x) = nothing
 _pat_replacer(x::AbstractChar) = isequal(x)
 _pat_replacer(x::Union{Tuple{Vararg{AbstractChar}},AbstractVector{<:AbstractChar},Set{<:AbstractChar}}) = in(x)
 
-function replace(str::String, pat_repl::Vararg{Pair,N}; count::Integer=typemax(Int)) where N
-    count == 0 && return str
+# note: leave str untyped here to make it easier for packages like StringViews to hook in
+function _replace_init(str, pat_repl::NTuple{N, Pair}, count::Int) where N
     count < 0 && throw(DomainError(count, "`count` must be non-negative."))
     n = 1
     e1 = nextind(str, lastindex(str)) # sizeof(str)
@@ -697,11 +697,11 @@ function replace(str::String, pat_repl::Vararg{Pair,N}; count::Integer=typemax(I
         r isa Int && (r = r:r) # findnext / performance fix
         return r
     end
-    if all(>(e1), map(first, rs))
-        foreach(_free_pat_replacer, patterns)
-        return str
-    end
-    out = IOBuffer(sizehint=floor(Int, 1.2sizeof(str)))
+    return patterns, replaces, rs, all(>(e1), map(first, rs))
+end
+
+# note: leave str untyped here to make it easier for packages like StringViews to hook in
+function _replace_finish(out::IO, str, count::Int, patterns::NTuple{N}, replaces::NTuple{N}, rs) where N
     while true
         p = argmin(map(first, rs)) # TODO: or argmin(rs), to pick the shortest first match ?
         r = rs[p]
@@ -737,12 +737,34 @@ function replace(str::String, pat_repl::Vararg{Pair,N}; count::Integer=typemax(I
     end
     foreach(_free_pat_replacer, patterns)
     write(out, SubString(str, i))
-    return String(take!(out))
+    return out
+end
+
+# note: leave str untyped here to make it easier for packages like StringViews to hook in
+function _replace_io(out::IO, retval, str, pat_repl::Pair...; count::Integer=typemax(Int))
+    count == 0 && return out
+    patterns, replaces, rs, notfound = _replace_init(str, pat_repl, count)
+    if notfound
+        foreach(_free_pat_replacer, patterns)
+        return out
+    end
+    return _replace_finish(out, str, count, patterns, replaces, rs)
 end
 
+# note: leave str untyped here to make it easier for packages like StringViews to hook in
+function _replace_str(str, pat_repl::Pair...; count::Integer=typemax(Int))
+    count == 0 && return str
+    patterns, replaces, rs, notfound = _replace_init(str, pat_repl, count)
+    if notfound
+        foreach(_free_pat_replacer, patterns)
+        return str
+    end
+    out = IOBuffer(sizehint=floor(Int, 1.2sizeof(str)))
+    return String(take!(_replace_finish(out, str, count, patterns, replaces, rs)))
+end
 
 """
-    replace(s::AbstractString, pat=>r, [pat2=>r2, ...]; [count::Integer])
+    replace([out::IO], s::AbstractString, pat=>r, [pat2=>r2, ...]; [count::Integer])
 
 Search for the given pattern `pat` in `s`, and replace each occurrence with `r`.
 If `count` is provided, replace at most `count` occurrences.
@@ -755,13 +777,21 @@ If `pat` is a regular expression and `r` is a [`SubstitutionString`](@ref), then
 references in `r` are replaced with the corresponding matched text.
 To remove instances of `pat` from `string`, set `r` to the empty `String` (`""`).
 
+The return value is a new string with the replacements.  If the `out::IO` argument
+is supplied, the transformed string is instead written to `out` (returning `out`).
+(For example, this can be used in conjunction with [`IOBuffer`](@ref) to re-use
+an pre-allocated buffer array in-place.)
+
 Multiple patterns can be specified, and they will be applied left-to-right
 simultaneously, so only one pattern will be applied to any character, and the
 patterns will only be applied to the input text, not the replacements.
 
 !!! compat "Julia 1.7"
     Support for multiple patterns requires version 1.7.
 
+!!! compat "Julia 1.10"
+    The `out::IO` argument requires version 1.10.
+
 # Examples
 ```jldoctest
 julia> replace("Python is a programming language.", "Python" => "Julia")
@@ -780,8 +810,18 @@ julia> replace("abcabc", "a" => "b", "b" => "c", r".+" => "a")
 "bca"
 ```
 """
+replace(out::IO, s::AbstractString, pat_f::Pair...; count=typemax(Int)) =
+    _replace_io(out, String(s), pat_f..., count=count)
+
 replace(s::AbstractString, pat_f::Pair...; count=typemax(Int)) =
-    replace(String(s), pat_f..., count=count)
+    _replace_str(String(s), pat_f..., count=count)
+
+# no copy needed for SubString{String}
+replace(out::IO, s::SubString{String}, pat_f::Pair...; count=typemax(Int)) =
+    _replace_io(out, s, pat_f..., count=count)
+replace(s::SubString{String}, pat_f::Pair...; count=typemax(Int)) =
+    _replace_str(s, pat_f..., count=count)
+
 
 # TODO: allow transform as the first argument to replace?
 

doc/src/base/strings.md

@@ -51,7 +51,7 @@ Base.findlast(::AbstractChar, ::AbstractString)
 Base.findprev(::AbstractString, ::AbstractString, ::Integer)
 Base.occursin
 Base.reverse(::Union{String,SubString{String}})
-Base.replace(s::AbstractString, ::Pair...)
+Base.replace(::IO, s::AbstractString, ::Pair...)
 Base.eachsplit
 Base.split
 Base.rsplit