From: Jim Weirich <jim@...>
Date: 2006-05-22T23:02:06+09:00
Subject: Re: rubynuby - confused by method name "inject"

Regg Mr wrote:

Two points:

> Seems like "sum" would have been a better name.

Unless the operator isn't + ...

    [1,2,3].inject { |left, right| left * right }
      # =>  1*2*3

    "A::B".split("::").inject(Object) { |left, right| 
left.const_get(right) }
      # =>  Object.const_get("A").const_get("B")

    (2..n).inject(1) { |left, right| left * right }
      # => n! => 2*3* ... * n

> Also
> 
> [1,2,3].each {|a| b += a}
> 
> is easier to read ...for me.

Perhaps, but there is a fundamental difference between the inject and 
each versions.  The "each" verison is procedural.  It defines state (the 
value of b) and how that state changes in each iteration (b += a).

The "inject" version is functional.  There are no extra state variables 
in our code that need initialization.  And the expression itself is the 
value, rather than having a side effect on a local variable.

Not that one way is better than the other, just noting differences.

-- Jim Weirich


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