From: merch-redmine@...
Date: 2019-02-19T15:15:48+00:00
Subject: [ruby-core:91594] [Ruby trunk Feature#15612] A construct to restrict the scope of local variables

Issue #15612 has been updated by jeremyevans0 (Jeremy Evans).


sawa (Tsuyoshi Sawada) wrote:
> In order to improve readability of the code by explicitly indicating the scope of such local variables, and to avoid pollution by the variable, I propose to have some construct to restrict the scope of local variables.
> 
> One possibility, without adding a new keyword to the current syntax, is to use the `begin`...`end` construct. The expected behavior would be:
> 
> ```ruby
> begin
>   foo = "foo"
>   foo # => "foo"
> end
> foo # => `nil`, or "Undefined local variable or method error"
> ```

This would definitely break existing code.  There is a lot of code that expects to be able to access local variables first assigned inside a begin/end block after the begin/end block.

As blocks already do what you want, why not just:

```ruby
tap do
  foo = "foo"
  foo # => "foo"
end
foo # => NameError
```

```ruby
foo = "bar"
tap do
  foo = "foo"
  foo # => "foo"
end
foo # => "foo"
```

You can substitute another method that yields once for `tap` if you want.

----------------------------------------
Feature #15612: A construct to restrict the scope of local variables
https://bugs.ruby-lang.org/issues/15612#change-76856

* Author: sawa (Tsuyoshi Sawada)
* Status: Feedback
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
We sometimes have local variables that are to be used only to keep track of some temporal states/values during a short routine:

```ruby
...
foo = some_initial_value
some_routine_that_uses_foo
...
```

Currently, the scope of local variables are either a proc, a block, `loop` body, a method definition, or a class/module definition, but such routines are sometimes just only a part of them.

In order to improve readability of the code by explicitly indicating the scope of such local variables, and to avoid pollution by the variable, I propose to have some construct to restrict the scope of local variables.

One possibility, without adding a new keyword to the current syntax, is to use the `begin`...`end` construct. The expected behavior would be:

```ruby
begin
  foo = "foo"
  foo # => "foo"
end
foo # => `nil`, or "Undefined local variable or method error"
```

```ruby
foo = "bar"
begin
  foo = "foo"
  foo # => "foo"
end
foo # => "bar"
```

Or, does this break the existing code too much? If so, can a new construct be added to the current syntax?




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