From: Yukihiro Matsumoto <matz@...>
Date: 2011-07-26T14:24:38+09:00
Subject: Re: Why aren't string literals treated similarly to symbols?

Hi,

It's because Ruby strings are mutable, just like array expression
makes a new instance of Array everytime.  On the other hand, symbols
are immutable.

							matz.

In message "Re: Why aren't string literals treated similarly to symbols?"
    on Tue, 26 Jul 2011 14:16:20 +0900, Jeremy Bopp <jeremy@bopp.net> writes:

|Explaining the difference between symbols and strings got me wondering
|why string literals aren't treated similarly to symbols by the
|interpreter.  To be clear it seems that string literals could be
|allocated 1 time each, where duplicates simply reference the first
|created instance.
|
|The trick would be to make each reference to the literal a dup of the
|singular, hidden instance.  With the COW semantics that dup'd strings
|have (or should have), this should be a more memory efficient way to
|deal with programs that have many instances of a string literal.
|
|One such possibly common place that could benefit from this optimization
|would be within frequently called methods or iterated loops that
|directly use string literals for read-only purposes.  If a developer
|wants to avoid the allocation problem of string literals as things
|currently stand, he/she would have to be aware of this problem first and
|then find ways to push his/her literals into constants or other exterior
|references.
|
|For example:
|
|1.upto(2) do
|  string = "example"
|  puts string
|end
|
|Unless I misunderstand the current implementation in MRI, a loop such as
|the one above would needlessly create a new instance of "good" for every
|pass through the loop.  One possible fix would be something like:
|
|string = "example"
|1.upto(2) do
|  puts string
|end
|
|In this trivial case, the solution is good enough, but the general case
|requires more knowledge about how to optimize for the interpreter than
|should be necessary.  I'm probably missing something obvious, so if
|anyone knows what it is, please point it out.  Maybe MRI already does
|this obvious thing.
|
|-Jeremy