From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2026-02-05T20:29:06+00:00
Subject: [ruby-core:124692] [Ruby Bug#21864] Inconsistencies in type coercion error messages for integers

Issue #21864 has been updated by byroot (Jean Boussier).


I'm working a a small refactor: https://github.com/ruby/ruby/pull/16078

I have to battle a bit with some test assertions, but it's pretty simple.

----------------------------------------
Bug #21864: Inconsistencies in type coercion error messages for integers
https://bugs.ruby-lang.org/issues/21864#change-116285

* Author: herwin (Herwin W)
* Status: Open
* ruby -v: ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [x86_64-linux], but consisten since at least Ruby 3.2, haven't checked older releases
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
Some context in https://github.com/ruby/spec/pull/1345, all code snippets are run using Ruby 4.0.1 on a 64bit Linux (Debian) system, unless stated otherwise.

Ruby has some generic type coercion error message. For example:
```ruby
File.truncate(var, 1)
```
Depending on the type of `var`, it can generate error messages like:
```
no implicit conversion of Integer into String (TypeError)
no implicit conversion of false into String (TypeError)
```
In general `true`, `false` and `nil` print the string representation of the object, anything else prints the class of the object. One could argue that this is inconsistent, but it's probably better than printing `NilClass` in the error (something I've recently seen happen in Natalie and TruffleRuby, I would guess JRuby occasionally has this issue as well, but I haven't looked for it. The exact error messages are often missing in the Ruby specs).

The conversion to integer is weird.
```ruby
File.truncate("/dev/zero", var)
```
Anything other than `nil` gets pretty much the same output as before:
```
no implicit conversion of Symbol into Integer (TypeError)
no implicit conversion of false into Integer (TypeError
```
But this is where nil has a special path:
```
no implicit conversion from nil to integer (TypeError)
```
Now it's usng "from .. to" instead of "of .. into", and `integer` is written in lower case.

But, this message is not consistent either, based on the size of `off_t`, where the coercion uses either `rb_num2long` or `rb_num2ll`, which have different checks for `nil`:
```c
// Taken from commit 86dba8cfaeabb3b86df921da24b3243b9ce4ab2a
long
rb_num2long(VALUE val)
{
  again:
    if (NIL_P(val)) {
        rb_raise(rb_eTypeError, "no implicit conversion from nil to integer");
    }

LONG_LONG
rb_num2ll(VALUE val)
{ 
    if (NIL_P(val)) {
        rb_raise(rb_eTypeError, "no implicit conversion from nil");
    }
```
That last one has some internal checks for other types, with more inconsistent error messages:
```c
rb_raise(rb_eTypeError, "no implicit conversion from string");
rb_raise(rb_eTypeError, "no implicit conversion from boolean");
```
That last one looks like the only error message to mention the term `boolean`.

IMHO the first message type is the clearest, so I would propose to write every coercion failure in this way:
```ruby
type = value.nil? || value == true || value == "false" ? value.inspect : value.class
klass = "String" # Or Integer, or ...
"no implicit conversion of #{type} into #{klass}"
```



-- 
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