From: "hanazuki (Kasumi Hanazuki) via ruby-core" <ruby-core@...>
Date: 2026-10-05T15:44:48+00:00
Subject: [ruby-core:126927] [Ruby Bug#22407] IO::Buffer#set_value does not call to_int for 128-bit values

Issue #22407 has been reported by hanazuki (Kasumi Hanazuki).

----------------------------------------
Bug #22407: IO::Buffer#set_value does not call to_int for 128-bit values
https://bugs.ruby-lang.org/issues/22407

* Author: hanazuki (Kasumi Hanazuki)
* Status: Open
* ruby -v: ruby 4.1.0dev (2026-10-05T15:26:55Z master 2c1e694a53) +PRISM [x86_64-linux]
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
IO::Buffer gained support for reading and writing 128-bit integers (:u128, :U128, :s128, and :S128) in Ruby 4.0 (commit:a7dc53b91c8475323b34d5a332fdb25d190e277d).
Unlike the other smaller integer types, IO::Buffer#set_value does not call to_int on non-Integer values for the 128-bit types. Same for #set_values.

```ruby
IntegerLike = Data.define(:value) do
  def to_int = value
end

buf = IO::Buffer.new(16)
buf.set_value(:u64, 0, IntegerLike.new(42))
buf.set_value(:u128, 0, IntegerLike.new(42))  # => not an integer (TypeError)
```

Hence the 128-bit integer types do not satisfy this statement in the method's documentation:
> Note that if the type is integer and value is Float, the implicit truncation is performed



-- 
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