Any reason Enum.first and Enum.rest are not implemented?

[Sam Vervaeck]

Hi,

I've found List.first and List.rest, but I couldn't find Enum.first and Enum.rest. Is there any reason this is only implemented for lists? I can think of a few cases were this would be useful. Any recursive algorithm that runs following the prescription "take one element out the bunch, process it, and take care of the rest later" would, I think, benefit from it.

Kind regards,

Sam

[Sam Vervaeck]

Correction: there is no `List.rest`. Using the same reasoning as below, I think this would be useful, too.

Op donderdag 16 februari 2017 12:02:24 UTC+1 schreef Sam Vervaeck:

[José Valim]

Because enumerables have no guarantee of ordering, so the notion of first can be misleading. You can use Enum.at(..., 0) but also with the disclaimer that it can be anything within a data-structure that does not provide order.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Peter Hamilton]

I'd support Enum.pop, which would return an element and an new enumerable without the element.

On Thu, Feb 16, 2017 at 3:20 AM José Valim <jose....@plataformatec.com.br> wrote:

Because enumerables have no guarantee of ordering, so the notion of first can be misleading. You can use Enum.at(..., 0) but also with the disclaimer that it can be anything within a data-structure that does not provide order.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

On Thu, Feb 16, 2017 at 12:02 PM, Sam Vervaeck <vervae...@skynet.be> wrote:

Hi,

I've found List.first and List.rest, but I couldn't find Enum.first and Enum.rest. Is there any reason this is only implemented for lists? I can think of a few cases were this would be useful. Any recursive algorithm that runs following the prescription "take one element out the bunch, process it, and take care of the rest later" would, I think, benefit from it.

Kind regards,

Sam

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[Tallak Tveide]

stream_split would do something like that. The tail is stored in a continuation function, so i'm not sure if this is 'good code', and i'd not vouch for putting something like that in stdlib without a thorough analysis (eg covering issues related to cleaning up the enumerable if the tail is not iterated after)

https://hex.pm/packages/stream_split

For simple cases though it works well :)

[Sam Vervaeck]

Seems like my mail got lost in my outbox. Attempt #2.

I agree with Peter Hamilton, a Enum.pop method would be quite nice, though I understand the difficulties.

Sam

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