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Message from discussion Performance problem with for-expression
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Rüdiger Klaehn  
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 More options Apr 25 2012, 3:28 pm
From: Rüdiger Klaehn <rkla...@googlemail.com>
Date: Wed, 25 Apr 2012 21:28:10 +0200
Local: Wed, Apr 25 2012 3:28 pm
Subject: Re: [scala-user] Performance problem with for-expression
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On Wed, Apr 25, 2012 at 9:17 PM, Roland Kuhn <goo...@rkuhn.info> wrote:
> Hi Rüdiger,

> On Apr 25, 2012, at 21:12 , Rüdiger Klaehn wrote:

>> I guess the reify macro is part of scala 2.10? My scala console
>> (2.9.1.final) does not know it. The only way to desugar a for loop is
>> to do scala -Xprint:typer -e "..."

> yes, it’s 2.10.

>> I think that the behavior is very surprising and unintuitive. Is there
>> a reason the variable declaration can not be just moved into the
>> closure during for expresison desugaring?

>> I guess I have to go over many lines of code tomorrow and see if there
>> are any occurrences of that pattern.

> As I said, I was also surprised. My guess is that the wrapping inside a Tuple2 (and hence the map() operation) is necessary in the general case to make both x and i available to the code down-stream.

Well, I guess it's just another thing one needs to be aware of.

It wouldn't be so bad if it would be wrapped like (k, (v,x)). But an
unnecessary call to hashCode is a real pain in many cases, especially
in a language like scala where almost everything overrides hashCode.


 
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