Re: std::string class instance are immutable or not??

* Alf P. Steinbach:


Oops, I forgot to comment on that.

Yes, it seems '+=' has inefficient implementations in Java and C#, but the
inefficient implementations are not inefficient because '+=' is costly for
immutable strings, as you wrote; on the contrary, '+=', as opposed to infix '+',
allows for maximum efficiency.

The Java and C# '+=' ops are just inefficient silly implementations.

For a faster implementation of '+=' for immutable strings you might look at (old
code and never quite finished) <url: http://alfsstringvalue.sourceforge.net/>;
of course, when I wrote that page & code, pointing to Java and C# for
efficiency, I didn't know that Java and C# are so inefficient! :-)

And by the way, in the test programs I now see that the C++ version had just
half the number of operations, which made C++ look very very efficient in
comparision; doubling the number of operations to the same as for Java and C#
makes it just somewhat more efficient than C#:

<results language="C++">
C:\temp> a
Infix '+' : 0.3910
concat : 0.0000
'+=' operator: 0.0000

C:\temp> a
Infix '+' : 0.3290
concat : 0.0160
'+=' operator: 0.0000

C:\temp> a
Infix '+' : 0.3280
concat : 0.0000
'+=' operator: 0.0000

C:\temp>
</results>

Cheers & hth.,

- Alf