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[Sergey Gromov]

Fri, 10 Oct 2008 10:37:28 -0500,
Andrei Alexandrescu wrote:
> Denis Koroskin wrote:
> > On Fri, 10 Oct 2008 19:19:45 +0400, Sergey Gromov 
> > <snake.scaly at gmail.com> wrote:
> > 
> >> Fri, 10 Oct 2008 19:10:19 +0400,
> >> Denis Koroskin wrote:
> >>> On Fri, 10 Oct 2008 18:33:43 +0400, Andrei Alexandrescu
> >>> <SeeWebsiteForEmail at erdani.org> wrote:
> >>>
> >>> > Sergey Gromov wrote:
> >>> >> I'd also like
> >>> >>   "foo" ~ text ~ "bar"
> >>> >> to become something like
> >>> >>   (new Array!(char)) ~= "foo" ~= text ~= "bar"
> >>> >> that is what Java does to string concatenation.  Sugar doesn't 
> >>> seem to
> >>> >> couple well with a purely library type.
> >>>
> >>> I doubt that. Java strings are immutable, their length can't be changed
> >>> either (i.e. they are a direct analog of a proposed invariant(char)[]).
> >>> Concatanating Java strings don't turn them into array, and it is dead
> >>> slow. Every sane person uses StringBuilder instead.
> >>
> >> Java compiler substitutes
> >>
> >> "foo" + text + "bar"
> >>
> >> with
> >>
> >> new StringBuilder().append("foo").append(text).append("bar").toString()
> >>
> >> all by itself because both String and StringBuilder are built-in
> >> classes.
> > 
> > Yes, you are right. From The Java Language Specification, 3rd edition:
> > 
> >> To increase the performance of repeated string concatenation,
> >> a Java compiler may use the StringBuffer class or a similar technique
> >> to reduce the number of intermediate String objects that are created
> >> by evaluation of an expression.
> 
> But that doesn't require StringBuffer to be part of the language. With 
> literals, the compiler can do whatever magic it wants.

They're no literals.  They're String objects.  Try this:

public class test {
 public static void main(String[] args) {
  String s = "foo" + args[0] + "bar" + args[1];
 }
}

$ javac test.java
$ javap -c test

Though you are right in the sense that the result of this expression is 
still String, StringBuilder can be replaced with anything else or not 
used at all.