[ruby-core:91596] [Ruby trunk Feature#15612] A construct to restrict the scope of local variables

Issue #15612 has been updated by duerst (Martin D端rst).


On top of what others have said, methods in Ruby should normally be quite short. If you have a method that's so long that you think you need restricted scopes for local variables, you should look at how to split the code into several methods.

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Feature #15612: A construct to restrict the scope of local variables
https://bugs.ruby-lang.org/issues/15612#change-76858

* 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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