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Comment by phzbOx | Hacker News Reader

  rand(1..10)

is now possible, cool!

Also:

  'est'.prepend('t') == 'test'

might be useful.

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Why is

  "est".prepend('t')

more useful than

  "t" + "est"

? I don't see why a method for prepending to a string is necessary, when it is so simple anyway...

And random with a range parameter is useful shorthand.

Anyway, I'm more enthusiastic about performance improvements where file loading is concerned.

Sometime it's easier to chain with other functions and, depending of the situation, it might make the code easier to read.

More useful? It does a different thing, just like String#+ doesn't do the same thing as String <<.

They are not exchanges for each other. Rather - they are complements.

Not to mention more verb like - and thus descriptive.

First, let's say you subclassed String or have a delegate. obj.prepend(str) will adjust obj in place rather than create an all new String object (as str + obj would). This may be either desirable or critical, depending on what you're doing.

Second, prepend is a lot faster than using + in this case. As in, a simple prepend runs in a mere 1.9% of the time (in a benchmark I just ran). Why? Fewer new objects are being created. And that means easier and fewer GC runs too.

Update: I think there is something slightly bust since on 1.9.2 using + handily beats prepend on 1.9.3. But GC has changed a lot. I'll retest on RC1 rather than preview1 ;-)

Good point; I did not consider conserving objects and the overhead of allocation/initialization versus reallocation.

#prepend replaces in place? There's no #prepend! ?

No.

Conventionally, "bang" methods should only be created as 'dangerous' versions of non-bang methods. There was no non-bang method to make a 'dangerous' version of in this case so it's non-bang by default. This is a commonly misunderstood naming convention in Ruby (and I dare say I don't even understand all the intricacies!)

There are quite a few examples of this in Ruby. For example, Array#keep_if which changes an array in place.

I guess I misunderstood your definition of "in place". That jives with what I've understood about Ruby so far.

That would be redundant, since there would be no difference from String#+.

How does String#prepend compare to String#insert in your benchmarks? eg. "bc".insert(0, "a") # => "abc"

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