[ruby-core:98092] [Ruby master Feature#13820] Add a nil coalescing operator

Issue #13820 has been updated by sawa (Tsuyoshi Sawada).


Your proposal to distinguish `nil` from `false` is ad hoc, and is not a real solution for your use case, which is to add a value to a hash only when it does not yet have a corresponding key.

Following your way of doing it, you would still not be able to distinguish `opts1` that explicitly has a key-value pair `:foo` => `nil` and `opts2` that lacks such pair.

```ruby
opts1 = {foo: nil}
opts2 = {}
```

Particularly, applying your code to update `opts1` would overwrite the explicit `nil` value:

```ruby
opts1[:foo] ||= "foo"
```

Ruby is aware of such use case, and has already prepared a real solution: the `Hash#key?` method. The correct way of doing it is:

```ruby
opts1[:foo] = "foo" unless opts1.key?(:foo)
```


----------------------------------------
Feature #13820: Add a nil coalescing operator
https://bugs.ruby-lang.org/issues/13820#change-85328

* Author: williamn (William Newbery)
* Status: Open
* Priority: Normal
----------------------------------------
It would be nice if Ruby had an operator that only considered `nil` as false, like the null coalescing operators or "Logical Defined-Or operator" (Perl) found in some other languages. Ive seen things like `//` and `//=`m `??` and `??=`, or `?:` used for this.

This would work like `||` and `||=` for short circuiting etc. except that only `nil` is considered a false condition.

While Ruby considers only "false" and "nil" as false, with everything else true ("", [], {}, etc.) I still find occasionally people trip up when using logical or, `||` and `||=` when the value may be false.


```ruby
a = 0     || 55 # = 0 Ruby already considers 0, "", etc. as true (oter languages do differ a lot here)
a = 0     ?? 55 # = 0 So no change here
a = nil   || 55 # = 55, nil is false so right side is evaulated.
a = nil   ?? 55 # = 55, again no change
a = false || 55 # = 55, however false is false for logical or
a = false ?? 55 # = false, but its still a non-nil value
```


For example when doing things like:

```ruby
def lazy
  @lazy ||= compute_this
end


def fetch(id, **opts)
  host  = opts[:host] || default_host
  https = opts[:https] || true
  port  = opts[:port] || (https ? 443 : 80)
  ...
```

Normally the intention is to use a default value or compute an action if no value is provided, which if the value may be false then requires special handling, or sometimes is missed and results in a bug.



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>