Bug #18957: StringIO#printf doesn't ignore initial String value

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 3.0.3
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[andrykonchin (Andrew Konchin)]

I've noticed that StringIO#printf diverges from IO#printf in the following way:

IO:

File.write("printf.txt", "1234567890")
f = File.open("printf.txt", "w+")
f.printf("%s", "abc")
f.rewind
f.gets
# => "abc"

StringIO:

io = StringIO.new("1234567890")
io.printf("%s", "abc")
io.rewind
io.gets
=> "abc4567890"

So File opened in a w mode "truncates" existing file content but StirngIO (by default) doesn't.

I would expect StringIO behaves in the same way.

[mame (Yusuke Endoh)]

StringIO behaves like File.open with an r+ mode.

File.write("printf.txt", "1234567890")
f = File.open("printf.txt", "r+")
f.printf("%s", "abc")
f.rewind
p f.gets #=> "abc4567890"

Is there any reason for you to expect it to be the same as w+ mode instead of r+?

[andrykonchin (Andrew Konchin)]

Good point. I overlooked the difference between r+ and w+. Thank you for clarification.

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Rejected