From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2023-12-06T15:33:22+00:00
Subject: [ruby-core:115609] [Ruby master Bug#20043] `defined?` checks for method existence but only sometimes

Issue #20043 has been updated by byroot (Jean Boussier).


> Is there any use case for defined? besides those?

Instance variables for sure: `defined?(@ivar)`.

Also checking for super: `defined?(super)`.

Some people use it for a sequence of calls: `defined?(foo.bar.baz)`.


----------------------------------------
Bug #20043: `defined?` checks for method existence but only sometimes
https://bugs.ruby-lang.org/issues/20043#change-105540

* 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.



-- 
https://bugs.ruby-lang.org/
 ______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/postorius/lists/ruby-core.ml.ruby-lang.org/