[ruby-core:103373] [Ruby master Feature#17790] Have a way to clear a String without resetting its capacity

Issue #17790 has been updated by byroot (Jean Boussier).


> My feeling is handling the capacity in Ruby code feels wrong and like C++ code.

This is really meant for the few low level places where it matters. For context this came up when trying to optimize a StatsD client, which is quite a hotspot. 

More generally there are cases when you know you'll return a large String/Array/Hash, and you know the size in advance, and it can make sense to pre-reserve capacity rather than having it resized a dozen times. Amusingly enough the C API allow to create an array or hash with a specific capacity.

> IMHO we should really have a separate Buffer class and String class here.

Possibly yes. StringIO is kind of meant to be that buffer class, but it's not always easier to use, and often is slower than using a string.

> I think clear(shrink: true/false) would be fine to add.

I think it would be good, but would also require a `String#resize(capacity)` as well.

So the pattern would be:

```
buffer = String.new(encoding: Encoding::BINARY, capacity: 1024)
loop do

  # do your thing
  buffer.clear(shrink: false)
  buffer.resize(1024)
end
``` 

----------------------------------------
Feature #17790: Have a way to clear a String without resetting its capacity
https://bugs.ruby-lang.org/issues/17790#change-91466

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
----------------------------------------
In some tight loop it can be useful to re-use a buffer string. For instance:

```ruby
buffer = String.new(encoding: Encoding::BINARY, capacity: 1024)

10.times do
  build_next_packet(buffer)
  udp_socket.send(buffer)
  buffer.clear
end
```

Currently `Array#clear` preserve the Array capacity, but `String#clear` doesn't:

```ruby
>> puts ObjectSpace.dump(Array.new(20).clear)
{"address":"0x7fd3260a1558", "type":"ARRAY", "class":"0x7fd3230972e0", "length":0, "memsize":200, "flags":{"wb_protected":true}}
>> puts ObjectSpace.dump(String.new(encoding: Encoding::BINARY, capacity: 1024).clear)
{"address":"0x7fd322a8a320", "type":"STRING", "class":"0x7fd3230b75b8", "embedded":true, "bytesize":0, "value":"", "memsize":40, "flags":{"wb_protected":true}}
```

It would be useful if `String#clear` wouldn't free allocated memory, but if it's a backward compatibility concern to change it, then maybe another method could make sense?




-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>