From: Sean O'Halpin <sean.ohalpin@...>
Date: 2006-06-17T04:54:47+09:00
Subject: Re: Symbol#to_proc Problem

[snip Elliot trying to have his cake and eat it ;)]

Think about what you're trying to do here.

Applying map on its own to both input data structures gives you:

{ 1=>2, 3=>4}.map #=> [[1,2], [3,4]]
[[1,2,3], [4,5,6], [7,8,9]].map #=> [[1,2,3], [4,5,6], [7,8,9]]

i.e. in both cases you are effectively mapping an array of arrays.

In the &:foo case, you want to apply the proc to the first element of
each array,
with subsequent elements as arguments. In the &:reverse case, you want to apply
the proc to each array as a whole. How can the lambda in the to_proc
method know which case is which?

You might be able to devise a hack to check the arity of the methods
involved, but even that is effectively guess work. On top of that,
using Symbol.to_proc in this way is very inefficient compared to using
blocks.

IMHO this is one of those clever hacks that shouldn't make it into
production code.

Regards,
Sean