From: Justin Collins <justincollins@...>
Date: 2012-06-22T09:31:45+09:00
Subject: Re: inject was Benchmark obsession?

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On 06/21/2012 04:30 PM, Henry Maddocks wrote:
>
> On 21/06/2012, at 9:50 AM, Ryan Davis wrote:
>
>> Given #inject's other alias, #reduce, it is obvious that you don't 
>> use #inject for building up other objects. Even in a functional style 
>> of programming you'd _never_ see it building up anything. You'd see 
>> it REDUCING (folding) an object. If #inject is applied in a 
>> non-folding manner, it isn't functional, it is just dumb. Don't 
>> pretend otherwise (and if you do pretend otherwise, go read more 
>> books on lisp--start with SICP). The second I see a semicolon (or 
>> return) in an inject, I immediately suspect that someone is writing 
>> clevar/stupid code.
>>
>> I don't have any recent examples from the list, but I'm on record in 
>> multiple mediums ranting against people who use #inject improperly. 
>> I'll make up one based on examples I've seen time and time again:
>
> I come across this quite often, especially in Rails apps.
>
> a = {:list => [1,2,3,4]}
> b = {:list => [9,8,7,6,5]}
>
> c = [a,b]
>
> c.inject([]) {|memo, run| memo + run[:list] }
>
> I always cringe when I see it but I haven't found an alternative that 
> is as clear and concise.
> collect and flatten looks ugly. I'd love to be able to do...
>
> c.collect {|run| *run[:list]}
>
>
> Henry

You could move the array outside:

a = {:list => [1,2,3,4]}
b = {:list => [9,8,7,6,5]}

c = [a,b]

all = []

c.each { |h| all.concat h[:list] }

Saves a little memory, too?

-Justin

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    On 06/21/2012 04:30 PM, Henry Maddocks wrote:
    <blockquote cite="mid:4DD22DBC-73CF-44F1-B165-653D8B6C027A@me.com"
      type="cite"><br>
      <div>
        <div>On 21/06/2012, at 9:50 AM, Ryan Davis wrote:</div>
        <br>
        <blockquote type="cite">
          <div>Given #inject's other alias, #reduce, it is obvious that
            you don't use #inject for building up other objects. Even in
            a functional style of programming you'd _never_ see it
            building up anything. You'd see it REDUCING (folding) an
            object. If #inject is applied in a non-folding manner, it
            isn't functional, it is just dumb. Don't pretend otherwise
            (and if you do pretend otherwise, go read more books on
            lisp--start with SICP). The second I see a semicolon (or
            return) in an inject, I immediately suspect that someone is
            writing clevar/stupid code.<br>
            <br>
            I don't have any recent examples from the list, but I'm on
            record in multiple mediums ranting against people who use
            #inject improperly. I'll make up one based on examples I've
            seen time and time again:<br>
          </div>
        </blockquote>
        <br>
      </div>
      <div>I come across this quite often, especially in Rails apps.</div>
      <div><br>
        <font class="Apple-style-span" face="Courier">a = {:list =&gt;
          [1,2,3,4]}<br>
          b = {:list =&gt; [9,8,7,6,5]}<br>
          <br>
          c = [a,b]<br>
          <br>
          c.inject([]) {|memo, run| memo + run[:list] }&nbsp;<br>
        </font><br>
      </div>
      <div>I always cringe when I see it but I haven't found an
        alternative that is as clear and concise.&nbsp;</div>
      <div>collect and flatten looks ugly. I'd love to be able to do...</div>
      <div><br>
      </div>
      <div><font class="Apple-style-span" face="Courier">c.collect
          {|run| *run[:list]}</font></div>
      <div><br>
      </div>
      <div><br>
      </div>
      <div>Henry</div>
    </blockquote>
    <br>
    You could move the array outside:<br>
    <br>
    a = {:list =&gt; [1,2,3,4]}<br>
    b = {:list =&gt; [9,8,7,6,5]}<br>
    <br>
    c = [a,b]<br>
    <br>
    all = []<br>
    <br>
    c.each { |h| all.concat h[:list] }<br>
    <br>
    Saves a little memory, too?<br>
    <br>
    -Justin<br>
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