From: "yhara (Yutaka HARA)" <redmine@...>
Date: 2013-01-12T04:58:35+09:00
Subject: [ruby-core:51387] [ruby-trunk - Bug #7248] Shouldn't Enumerator::Lazy.new be private?


Issue #7248 has been updated by yhara (Yutaka HARA).

Assignee changed from yhara (Yutaka HARA) to marcandre (Marc-Andre Lafortune)

marcandre (Marc-Andre Lafortune) wrote:
> Oh, interesting.
> 
> I'll do my best to document it, then.
> 
Thanks!

> This leads to more questions, though:
> 
> 1) Is there a use case for the form without a block?
> 
> It's used internally (before calling lazy_set_method), but other than that I can't see a good use.
> 

That form is only for internal use.
You can remove the form without a block by replacing `Lazy.new(enum)'
with `Lazy.new(enum){|y, v| y<<v}'.

> 2) Is there a use case for specifying a symbol and arguments?
> 

Actually I did not know lazy_initialize can take a symbol :-p
So I'm not sure about how the symbol and arguments are used,
but it looks like for internal use.
According to svn annotate, it is introduced to implement lazy.cycle (r35028).

> Again, internally we call lazy_set_method, to the symbol and arguments are only used by inspect, right?
> 

That seems right.

> 3) Is there a good way to improve the `inspect` of such a lazy enum?
> 
>     p [11,12,13].filter_map{|i| i*i if i.even?} # => #<Enumerator::Lazy: #<Enumerator::Lazy: [1, 2, 3]>:each>
> 
> Notice the `each` and no appearance of `filter_map`
> 
> Doing `Lazy.new(self, :filter_map)` does not work and seems redundant.
> 
> 
> BTW, ultimately, I'm trying to see if Lazy.new can be adapted to accept a `size` lambda argument...

Well, I have no idea. It would be difficult to design Lazy.new which may take 
obj, block, symbol, args and size/size_fn...

BTW, I have a question. Document of to_enum says "see Enumerator#size=" but there is no such method. Is it a typo?
https://github.com/ruby/ruby/blob/e90ccd3beb0b9bf1125461ef68943578739bebbe/enumerator.c#L201

----------------------------------------
Bug #7248: Shouldn't Enumerator::Lazy.new be private?
https://bugs.ruby-lang.org/issues/7248#change-35364

Author: marcandre (Marc-Andre Lafortune)
Status: Assigned
Priority: Normal
Assignee: marcandre (Marc-Andre Lafortune)
Category: core
Target version: 2.0.0
ruby -v: ruby 2.0.0dev (2012-10-29 trunk 37380) [x86_64-darwin10.8.0]


Is there a reason why Enumerator::Lazy.new is not private?

Lazy enumerators should be created with `Enumerable#lazy`. Moreover, there is no doc, and it can give unexpected results too.


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