[ruby-core:95511] [Ruby master Feature#16275] Revert `.:` syntax

[daniel@dan42.com]

Issue #16275 has been updated by Dan0042 (Daniel DeLorme).


I'm also in favor of removing `.:` until a better "whole picture" is formed. Besides, that syntax encourages the idea that symbols are closely related to functional objects. And it looks like cuneiform.

For example, if we consider that `->` is a functional syntax for lambdas, we could adopt the '>' character as a common element of functional syntax in general. Below is a _very hypothetical_ example just to show that a whole-picture view could possibly lead to different results:

```
potential functional operators
!>      
&>      
(>      
*>      
+>      
,>      
->       lambda
/>      
:>word   :word.to_proc    
;>      
<>      
@>       
[>      
\>      
^>      
`>      
{>      
|>       pipeline
~>word   obj.method(:word)
~~>word  obj.instance_method(:word)

conflict / already used
">  string
'>  string
#>  comment
$>  stdout
%>  string
)>  greater-than
.>  greater-than
=>  hash literal
>>  right shift
?>  erb
]>  greater-than
}>  greater-than
```

----------------------------------------
Feature #16275: Revert `.:` syntax
https://bugs.ruby-lang.org/issues/16275#change-82287

* Author: naruse (Yui NARUSE)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
`obj.:method` is introduced at r66667 by #12125 and #13581.
It encourages the functional programming style in Ruby.

But this shorthand syntax is just for methods of `self` without arguments.
It causes another feature requests like #16273 (and lambda compositions like #15428).

Such features will introduce a new view of Ruby but no one illustrates the whole picture yet.
I worried about such patch work may cause a conflict with future expansion of functional programing style or a just a garbage feature.

`.:` syntax is introduced in 2.7.0 preview1, not released in production yet.
How about reverting at this time and re-introduce with a big picture.



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