make IOBuffer(array) writable by default

[bicycle1885]

IOBuffer(UInt8[]) is not writable by default while IOBuffer() is. This looks inconsistent to me, and so I'd like to make IOBuffer(array) writable by default. IOBuffer(string) is kept as-is because making it writable may result in an expected behavior.

[vtjnash]

This looks inconsistent to me

Why is this inconsistent? open is also usually read-only by default.

[bicycle1885]

One may expect IOBuffer() is a shorthand of IOBuffer(UInt8[]) but actually it isn't due to the difference of the writable flag. open is a function to open a file and so it is not directly related to IOBuffer's constructor. Also, in most cases, IOBuffer(array) calls are with writable=true:

~/v/julia (master|…) $ rg '=.*IOBuffer\(' base | rg -v "IOBuffer\(\)" | rg -v "\w+\(.*="
base/io.jl:julia> buf = IOBuffer("    text")
base/iobuffer.jl:    b = IOBuffer(StringVector(32), readable, writable)
base/printf.jl:    fmt = IOBuffer(fmt_len)
base/dates/io.jl:    io = IOBuffer(Vector{UInt8}(bufsize), true, true)
base/strings/basic.jl:    out = IOBuffer(StringVector(endof(s)),true,true)
base/strings/basic.jl:    out = IOBuffer(StringVector(endof(s)),true,true)
base/strings/io.jl:    s = IOBuffer(StringVector(size), true, true)
base/strings/io.jl:    s = IOBuffer(StringVector(tostr_sizehint(xs[1])), true, true)
base/strings/io.jl:julia> io = IOBuffer("Haho");
base/strings/io.jl:    buf = IOBuffer(StringVector(endpos), true, true)
base/strings/util.jl:    out = IOBuffer(StringVector(floor(Int, 1.2sizeof(str))), true, true)

[samoconnor]

related #24526

[StefanKarpinski]

Bump – can we make some progress here? @JeffBezanson has already approved so my merge finger is getting itchy...

[stevengj]

Read-only seems like a safer default here. (Note that most of the writable usages in Base employ the undocumented StringVector.) @vtjnash's analogy with open makes sense to me. Note that making it writable changes the behavior of take!, for example, so this is a breaking change.

Most of the cases where you pass a writable array seem to be just cases where you want a size hint, and it would be better in this case to actually have a sizehint parameter (e.g. so that it uses a StringVector).

Now that keywords are fast, can we just change the IOBuffer arguments into keywords? IOBuffer(array, writable=true) is a lot more readable than IOBuffer(array, true, true), and then we could add IOBuffer(sizehint=10).

[StefanKarpinski]

From triage: this should behave like open and use the same open_flags keyword pre-processing as open does with a few additional options like sizehint. There are a few other optional positional arguments that we may not want to expose as part of the public API of IOBuffer.