[Mono-list] C#/.NET Generics update and summary
Stefan Matthias Aust
Sat, 29 Mar 2003 12:48:16 +0100
David Jeske wrote:
> Since I'm very interested in C# Generics, in particular it's ability
> to improving typing and help close the performance gap with C/C++, I
> figured I'd post a summary of recent Generics information for anyone
> who is interested:
I'd also like to see generics (both in Java and C#) so I'd like to
comment on your compiled information. Thanks for your work.
For me, improved type safety is the more important point. By my
definition, a language like Java or C# must be considered statically
unsafe as lony as null pointer/reference exceptions or class
cast/invalid class exceptions can occur.
At least the latter can be worked around with generic types.
A more powerful type system (see for example nice.sf.net for a really
nice superset of Java which doesn't have these problems anymore) would
be required to get rid of null pointer exceptions.
> similar needs as C++ templates or Generic Java (GJC). Currently the
> performance of collections in .NET (or JVM) is similar to that of
> Python, Perl, or Smalltalk because collections involve runtime
> dynamic type casting.
Smalltalk - I know for sure - has no concept of static types, therefore
no concept for typecasts whatsoever and therfore has no such overhead
and its collections work with every type of object without any runtime
penalty. So I don't think that your comparison works. The performance
is worse because to regain static type-safeness, both Java and C# have
to inject runtime type checks into the getter methods.
Java furthermore suffers because you have to explicitely box and unbox
primitive types. It might be possible that .NET could provide faster
boxing and unboxing because the VM deals with this issue but I don't
know. As languages like Smalltalk have no primitives types and use
objects all the time, this penalty isn't there and collections in
Smalltalk are more efficient. (Of course, not having primitives
datatypes can cause larger memory footprint or less efficient
arithmetics in other parts of the program but that's a different story.
In fact, by using objects all the time, there's no integer overflow in
Smalltalk and the transition from small to large integers (with
unlimited precision) is transparent for the user.)
> Generics for .NET support runtime
> specialization into static code, eliminating the extra typechecks,
> and bringing the performance of collections closer to that of C/C++.
Support, but not require. As I understand the specification, it would
be pretty valid to use the same method as generic Java to fulfill the
specification. However, there's an opportunity to generate special
kinds of collections for primitive types.
It's still unclear for me what would be the better approach to spread
the use of generics. The Java way which says we will not change the VM
so that any code written with generic types will still run on old
installations (although not faster than the old non-generic-code) or the
.NET way which says you'll need a new VM (aka VES) but you might get
better performance in exchange.
> 5) How is C# Generics different from Generic Java?
Isn't the extended type system which is the foundation for C# generics
also more powerful that what Java has because its modeled after the ILX
requirements which shall help to generate more efficient code for
functional languages like F# (Ocaml) or Haskell(.NET)?
> "retrofit" with parametric type-specifications. Generic Java is
> rumored to be slated for the next Java release (1.5?) for which no
> date is set.
It's not a rumor but part of the release 1.5 plan AFAIK. The generics
compiler is already available, although that compiler doesn't feature
the other syntax changes (boxing, enums, foreach-statement etc), yet
which will also be introduced to 1.5 to probably should make Java to
catch up with C# again.
The Eclipse project announced to add generics to their compiler as part
of the 2.2 release which might be available in six months or so. Early
access versions are hopefully available is a few months.
Java 1.5 should be available in early 2004 with a beta which will
probably be released in July at the JavaOne conferrence (my guess, not
> run-time casts. Gyro, a reference implementation of Generic C#/CIL,
> is available as a patch to the Microsoft Shared Source CLI.
Does Gyro already has the mentioned CLI 2.0 and is there a measurable
Stefan Matthias Aust //
www.3plus4software.de // Inter Deum Et Diabolum Semper Musica Est