From: Ben Weissmann <bsw@...>
Date: 2013-01-24T13:39:08+09:00
Subject: [ruby-core:51614] Inconsistency between Enumerable#map and Enumerable#select

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Hey all,

I've found an inconsistency between Enumerable#map and Enumerable#select,
and i'm wondering what the rationale behind it is:

a = ['a', 'b', 'c']

a.each_with_index.select{|pr| p pr}
# prints:
# ["a", 0]
# ["b", 1]
# ["c", 2]

a.each_with_index.map{|pr| p pr}
# prints:
# "a"
# "b"
# "c"

I've posted this question to StackOverflow [1], and the responses point to
a difference between the implementation of select and map in both MRI and
Rubinius. Is there a rationale for this difference, and is
there documentation for which Enumerable methods use which implementation?

Thanks,
Ben
bsw@mit.edu

[1]
http://stackoverflow.com/questions/14492882/chaining-enumerators-that-yield-multiple-arguments

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<div dir=3D"ltr">Hey all,<div><br></div><div style>I&#39;ve found an incons=
istency between Enumerable#map and Enumerable#select, and i&#39;m wondering=
 what the rationale behind it is:</div><div style><br></div><div style><div=
>

a =3D [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;]</div><div><br></div><div>a.ea=
ch_with_index.select{|pr| p pr}</div><div># prints:</div><div># [&quot;a&qu=
ot;, 0]</div><div># [&quot;b&quot;, 1]</div><div># [&quot;c&quot;, 2]</div>

<div><br></div><div>a.each_with_index.map{|pr| p pr}</div><div># prints:</d=
iv><div># &quot;a&quot;</div><div># &quot;b&quot;</div><div># &quot;c&quot;=
</div><div><br></div><div style>I&#39;ve posted this question to StackOverf=
low [1], and the responses point to a difference between the implementation=
 of select and map in both MRI and Rubinius. Is there a rationale for this =
difference, and is there=A0documentation=A0for which Enumerable methods use=
 which implementation?</div>

<div style><br></div><div style>Thanks,</div><div style>Ben</div><div style=
><a href=3D"mailto:bsw@mit.edu">bsw@mit.edu</a></div><div style><br></div><=
div style>[1]=A0<a href=3D"http://stackoverflow.com/questions/14492882/chai=
ning-enumerators-that-yield-multiple-arguments">http://stackoverflow.com/qu=
estions/14492882/chaining-enumerators-that-yield-multiple-arguments</a></di=
v>

</div></div>

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