From: merch-redmine@...
Date: 2018-08-10T03:02:11+00:00
Subject: [ruby-core:88413] [Ruby trunk Feature#14975] String#append without changing receiver's encoding

Issue #14975 has been updated by jeremyevans0 (Jeremy Evans).


Making `String#<<` not change the encoding of the receiver may cause backward compatibility issues (raising an exception where an exception is not currently raised):

~~~ ruby
b = 'a'.force_encoding('BINARY')
u = "\u00ff".force_encoding('UTF-8')

# This currently results in b having UTF-8 encoding, since b is 7-bit.
# With this proposal, b would have BINARY encoding.
b << u

# This doesn't raise exception now, since b is now has UTF-8 encoding.
# With this proposal, an exception would be raised, since the
# encodings are not compatible can b is no longer 7-bit.
u << b
~~~

I think it may be worth adding support for this feature, but it should probably be a new method (maybe `#bconcat` since `#b` already returns a copy with binary encoding) to not break backwards compatibility.

----------------------------------------
Feature #14975: String#append without changing receiver's encoding
https://bugs.ruby-lang.org/issues/14975#change-73465

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
I'm not sure where this fits in, but in order to avoid garbage and superfluous function calls, is it possible that `String#<<`, `String#concat` or the (proposed) `String#append` can avoid changing the encoding of the receiver?

Right now it's very tricky to do this in a way that doesn't require extra allocations. Here is what I do:

```ruby
class Buffer < String
	BINARY = Encoding::BINARY
	
	def initialize
		super
		
		force_encoding(BINARY)
	end
	
	def << string
		if string.encoding == BINARY
			super(string)
		else
			super(string.b) # Requires extra allocation.
		end
		
		return self
	end
	
	alias concat <<
end
```

When the receiver is binary, but contains byte sequences, appending UTF_8 can fail:

```
"Foobar".b << "F����bar"
=> "FoobarF����bar"

> "F����bar".b << "F����bar"
Encoding::CompatibilityError: incompatible character encodings: ASCII-8BIT and UTF-8
```

So, it's not possible to append data, generally, and then call `force_encoding(Encoding::BINARY)`. One must ensure the string is binary before appending it.

It would be nice if there was a solution which didn't require additional allocations/copies/linear scans for what should basically be a `memcpy`.

See also: https://bugs.ruby-lang.org/issues/14033 and https://bugs.ruby-lang.org/issues/13626#note-3

There are two options to fix this:

1/ Don't change receiver encoding in any case.
2/ Apply 1, but only when receiver is using `Encoding::BINARY`




-- 
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