From: "Dan0042 (Daniel DeLorme) via ruby-core" <ruby-core@...>
Date: 2023-12-19T14:24:57+00:00
Subject: [ruby-core:115794] [Ruby master Bug#20043] `defined?` checks for method existence but only sometimes

Issue #20043 has been updated by Dan0042 (Daniel DeLorme).


I didn't know about this way of using `defined?` and it's interesting to me that we can check if multiple things are defined at once. Although the 3rd case below is another example that seems odd. But both that and `defined?([*a])` return "expression" since ruby 1.9, not 2.2

```ruby
x = 1
defined?(x) and defined?(y) and defined?(z) #=> nil
defined?([x, y, z])                         #=> nil (shorter!)
defined?(x && y && z)                       #=> "expression" (???)
defined?(x & y & z)                         #=> nil
```

----------------------------------------
Bug #20043: `defined?` checks for method existence but only sometimes
https://bugs.ruby-lang.org/issues/20043#change-105738

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.3.0dev (2023-12-05T21:25:34Z master 56eccb350b) [arm64-darwin23]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
When an expression is passed to `defined?`, it will _sometimes_ check if a method in a sub-expression is defined and sometimes it won't.

For example:

```
$ ./miniruby -e'p defined?(a)'
nil
$ ./miniruby -e'p defined?([a])'
nil
```

In the above case, Ruby will check whether or not the method `a` is defined, and it returns `nil`.  However, if you use a splat, it will not check:

```
$ ./miniruby -e'p defined?([*a])'
"expression"
```

The same thing seems to happen with method parameters:

```
$ ./miniruby -e'p defined?(itself)'
"method"
$ ./miniruby -e'p defined?(itself(a))'
nil
$ ./miniruby -e'p defined?(itself(*a))'
"method"
```

Oddly, `defined?` will check contents of arrays, but _won't_ check contents of hashes:

```
$ ./miniruby -e'p defined?([[[[a]]]])'
nil
$ ./miniruby -e'p defined?({ a => a })'
"expression"
```

I think all of the cases that refer to `a` should check whether or not `a` is defined regardless of splats or hashes.

---Files--------------------------------
clipboard-202312191405-owvpy.png (27.3 KB)


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