[ruby-core:108214] [Ruby master Feature#18690] Allow `Kernel#then` to take arguments

Issue #18690 has been reported by sawa (Tsuyoshi Sawada).

----------------------------------------
Feature #18690: Allow `Kernel#then` to take arguments
https://bugs.ruby-lang.org/issues/18690

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
----------------------------------------
`Kernel#then` passes the receiver to the block as its first positional argument.

```ruby
1.5.then{|x| Math.atan(x)}
```

I would like to propose to let `then` take arguments, which would be passed to the block as the other arguments.

```ruby
3.then(4){|x, y| Math.hypot(x, y)}
```

There are two uses. First, to separate bulky or repeated parameters from the routine. Instead of writing:

```ruby
honyarara.then{|x|
  foo(x)
  bar(fugafugafuga)
  baz(hogehogehoge)
  qux(x, fugafugafuga, hogehogehoge)
}
```

we can then write:

```ruby
honyarara.then(fugafugafuga, hogehogehoge){|x, y, z|
  foo(x)
  bar(y)
  baz(x)
  qux(x, y, z)
}
```

Second, to use a proc with multiple parameters when, for some reason, you do not want to define a method to do it:


```ruby
p = ->(x, y, z){
  foo(x)
  bar(y)
  baz(x)
  qux(x, y, z)
}

honyarara.then(fugafugafuga, hogehogehoge, &p)
```




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