From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2022-12-20T10:26:01+00:00
Subject: [ruby-core:111344] [Ruby master Feature#19245] Strict mode for Array#pack that doesn't silently truncate numbers that are too large for the given directive

Issue #19245 has been updated by byroot (Jean Boussier).





> The word ���specified��� makes confusion.



Apologies.



> Usually we don���t add ! for stricter behavior.



Indeed. If anything it's the version that silently truncate that would be the "more dangerous" version of it, which is usually what `!` suffix tend to mean in ruby-core. But that's not really an option. So I guess `strict: true` is the way to go.



----------------------------------------

Feature #19245: Strict mode for Array#pack that doesn't silently truncate numbers that are too large for the given directive

https://bugs.ruby-lang.org/issues/19245#change-100718



* Author: byroot (Jean Boussier)

* Status: Open

* Priority: Normal

----------------------------------------

```ruby

>> [256].pack("C").unpack1("C")

=> 0

>> [257].pack("C").unpack1("C")

=> 1

```



This is specified:



```ruby

  it "encodes the least significant 32 bits of a negative number" do

    [ [[-0x0000_0021], "\xdf\xff\xff\xff"],

      [[-0x0000_4321], "\xdf\xbc\xff\xff"],

      [[-0x0065_4321], "\xdf\xbc\x9a\xff"],

      [[-0x7865_4321], "\xdf\xbc\x9a\x87"]

    ].should be_computed_by(:pack, pack_format())

  end

```



But not documented in `Array#pack`.



I think that in many case this may lead to silent bugs.



### Possible solutions



We could have a strict version of `pack`, either `pack(template, strict: true)` or `pack!(template)`.



Or alternatively if we think this is never a desired behavior, we could change `pack` to first warn on truncation and later raise.











-- 

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