add sizehint keyword argument to IOBuffer (JuliaLang#25944)

NEWS.md

@@ -587,6 +587,9 @@ Library improvements
  like other `AbstractDict` subtypes and its constructors mirror the
  ones of `Dict`. ([#25210])
 
+ * `IOBuffer` can take the `sizehint` keyword argument to suggest a capacity of
+ the buffer ([#25944]).
+
 Compiler/Runtime improvements
 -----------------------------
 

base/iobuffer.jl

@@ -40,6 +40,7 @@ It may take optional keyword arguments:
 - `read`, `write`, `append`: restricts operations to the buffer; see `open` for details.
 - `truncate`: truncates the buffer size to zero length.
 - `maxsize`: specifies a size beyond which the buffer may not be grown.
+- `sizehint`: suggests a capacity of the buffer (`data` must implement `sizehint!(data, size)`).
 
 When `data` is not given, the buffer will be both readable and writable by default.
 
@@ -84,10 +85,14 @@ function IOBuffer(
  write::Union{Bool,Nothing}=nothing,
  append::Union{Bool,Nothing}=nothing,
  truncate::Union{Bool,Nothing}=nothing,
- maxsize::Integer=typemax(Int))
+ maxsize::Integer=typemax(Int),
+ sizehint::Union{Integer,Nothing}=nothing)
  if maxsize < 0
  throw(ArgumentError("negative maxsize: $(maxsize)"))
  end
+ if sizehint !== nothing
+ sizehint!(data, sizehint)
+ end
  flags = open_flags(read=read, write=write, append=append, truncate=truncate)
  buf = GenericIOBuffer(data, flags.read, flags.write, true, flags.append, Int(maxsize))
  if flags.truncate
@@ -101,8 +106,9 @@ function IOBuffer(;
  write::Union{Bool,Nothing}=true,
  append::Union{Bool,Nothing}=nothing,
  truncate::Union{Bool,Nothing}=true,
- maxsize::Integer=typemax(Int))
- size = maxsize == typemax(Int) ? 32 : Int(maxsize)
+ maxsize::Integer=typemax(Int),
+ sizehint::Union{Integer,Nothing}=nothing)
+ size = sizehint !== nothing ? Int(sizehint) : maxsize != typemax(Int) ? Int(maxsize) : 32
  flags = open_flags(read=read, write=write, append=append, truncate=truncate)
  buf = IOBuffer(
  StringVector(size),

base/strings/basic.jl

@@ -512,8 +512,7 @@ isascii(s::AbstractString) = all(isascii, s)
 ## string map, filter, has ##
 
 function map(f, s::AbstractString)
- out = IOBuffer(StringVector(sizeof(s)), read=true, write=true)
- truncate(out, 0)
+ out = IOBuffer(sizehint=sizeof(s))
  for c in s
  c′ = f(c)
  isa(c′, Char) || throw(ArgumentError(
@@ -525,8 +524,7 @@ function map(f, s::AbstractString)
 end
 
 function filter(f, s::AbstractString)
- out = IOBuffer(StringVector(sizeof(s)), read=true, write=true)
- truncate(out, 0)
+ out = IOBuffer(sizehint=sizeof(s))
  for c in s
  f(c) && write(out, c)
  end

base/strings/io.jl

@@ -81,10 +81,7 @@ julia> sprint(showcompact, 66.66666)
 ```
 """
 function sprint(f::Function, args...; context=nothing, sizehint::Integer=0)
- s = IOBuffer(StringVector(sizehint), read=true, write=true)
- # specialized version of truncate(s,0)
- s.size = 0
- s.ptr = 1
+ s = IOBuffer(sizehint=sizehint)
  if context !== nothing
  f(IOContext(s, context), args...)
  else
@@ -99,11 +96,11 @@ tostr_sizehint(x::Float64) = 20
 tostr_sizehint(x::Float32) = 12
 
 function print_to_string(xs...; env=nothing)
+ if isempty(xs)
+ return ""
+ end
  # specialized for performance reasons
- s = IOBuffer(StringVector(tostr_sizehint(xs[1])), read=true, write=true)
- # specialized version of truncate(s,0)
- s.size = 0
- s.ptr = 1
+ s = IOBuffer(sizehint=tostr_sizehint(xs[1]))
  if env !== nothing
  env_io = IOContext(s, env)
  for x in xs
@@ -436,8 +433,7 @@ Returns:
 function unindent(str::AbstractString, indent::Int; tabwidth=8)
  indent == 0 && return str
  # Note: this loses the type of the original string
- buf = IOBuffer(StringVector(sizeof(str)), read=true, write=true)
- truncate(buf,0)
+ buf = IOBuffer(sizehint=sizeof(str))
  cutting = true
  col = 0 # current column (0 based)
  for ch in str

base/strings/util.jl

@@ -383,9 +383,7 @@ function replace(str::String, pat_repl::Pair; count::Integer=typemax(Int))
  i = a = firstindex(str)
  r = coalesce(findnext(pattern,str,i), 0)
  j, k = first(r), last(r)
- out = IOBuffer(StringVector(floor(Int, 1.2sizeof(str))), read=true, write=true)
- out.size = 0
- out.ptr = 1
+ out = IOBuffer(sizehint=floor(Int, 1.2sizeof(str)))
  while j != 0
  if i == a || i <= k
  unsafe_write(out, pointer(str, i), UInt(j-i))