[Ironruby-core] Multiple overloads VS Inline casting

Peter Bacon Darwin bacondarwin at googlemail.com
Sun Jul 20 04:24:07 EDT 2008


Thanks Tomas.

 

From: ironruby-core-bounces at rubyforge.org
[mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Tomas Matousek
Sent: Saturday,19 July 19, 2008 23:10
To: ironruby-core at rubyforge.org
Subject: Re: [Ironruby-core] Multiple overloads VS Inline casting

 

If there is an implicit conversion from whatever types you need to convert
to BigDecimal then this single overload should be sufficient:

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, BigDecimal/*!*/ b, int n) 

 

The second overload you use now

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, object b, object n)

 

does conversions and call the first overload, right? In future the
conversions will be described by attributes on the first overload and the
second overload won't be necessary. It also depends how we define implicit
conversions for BigDecimal. If an arbitrary method has a BigDecimal
parameter should it be possible to pass Fixnum? If that is a common case
(maybe with some exemptions) it might be reasonable to define an implicit
conversion from Fixnum to BigDecimal. Then the single overload would handle
all cases. Otherwise you would need overloads from all types of "b"
parameter that this method can take.

 

Also, if you want to prevent allocation of BigDecimal for "b" parameter when
Fixnum is passed in (which might be a good optimization) you need 

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, int b, int n) 

 

overload.

 

Note that the implicit conversions and protocol attributes are not supported
right now. It will take some time to do so.

For now 

 

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, BigDecimal/*!*/ b, int n) 

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, object b, object n)

 

overloads with manual conversions might be good enough. If you want to
optimize add overloads for int and double, unless the only thing they do is
to allocate BigDecimal and call the first one. Then it doesn't make sense to
optimize them.

 

Tomas

 

From: ironruby-core-bounces at rubyforge.org
[mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Peter Bacon Darwin
Sent: Saturday, July 19, 2008 1:26 PM
To: ironruby-core at rubyforge.org
Subject: Re: [Ironruby-core] Multiple overloads VS Inline casting

 

So in the example I gave, what would be the preferred set of overloads?

Obviously from (1) there would be:

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, BigDecimal/*!*/ b, int n) ...

but what form should the "strongly typed overload" that you describe in (2)
take?

Cheers,

Pete

 

From: ironruby-core-bounces at rubyforge.org
[mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Tomas Matousek
Sent: Saturday,19 July 19, 2008 20:50
To: ironruby-core at rubyforge.org
Subject: Re: [Ironruby-core] Multiple overloads VS Inline casting

 

We are well aware of this issue and have a plan to solve it:

 

1)      You define overloads for type combinations that you want to
optimize. I'm going to improve class initializers to have a less overhead.
Even now though the initialization doesn't contribute significantly to
startup time.

2)      For the rest of the parameter type combinations whose performance is
not critical you define a strongly typed overload(s) that can accept all of
them. The conversions should happen automatically in the binder. There will
be some well defined conversions + a set of attributes to customize them.
The goal is not to perform type conversions imperatively in library code if
possible. The predefined conversions will follow Ruby conversion protocols
like to_i, to_s, etc. If a particular method doesn't support the default
conversion (Ruby library methods are inconsistent on what conversions are
used) or a there are multiple applicable conversions to chose from,
attributes would be available to specify the right one.

 

Tomas

 

From: ironruby-core-bounces at rubyforge.org
[mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Peter Bacon Darwin
Sent: Saturday, July 19, 2008 12:03 PM
To: ironruby-core at rubyforge.org
Subject: [Ironruby-core] Multiple overloads VS Inline casting

 

I have noticed in the libraries that are often methods that take multiple
parameters and each parameter can take a number of different types.  A
simple example, BigDecimal#add method has two parameters: a.add(b,n), where
a is BigDecimal, b needs to be compatible with BigDecimal and n needs to be
compatible with Fixnum.  In other words it is possible that b and n can be
one of [NotNull]BigDecimal/*!*/, [NotNull]BigInteger/*!*/, int, double and
object.  This leads to an implementation question.

 

Initially it seemed sensible to abstract out the conversion of these types -
except perhaps the best case ([NotNull]BigDecimal/*!*/ and int) - into a
helper method and then have just:

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, BigDecimal/*!*/ b, int n) ...

and

public static BigDecimal/*!*/ Add(CodeContext/*!*/ context, BigDecimal/*!*/
self, object b, object n) ...

In the second method you convert the parameters to the correct types and
pass them back to the first method.  This is basically what happens in the
current implementation of many of the Socket library methods.  This provides
a single place of conversion, which is particularly helpful given the
BigDecimal class has lots of methods that take this form that will all use
this conversion.  It makes the code readable and doesn't create masses of
overloads for the class.

 

After thinking about this for a bit I started to wonder about performance.
This style of method does not allow performance tricks in the DLR to benefit
the code.  If you have the type lookup inside the methods then that gets
called every single time those methods are called.

 

The other implementation idea then is to create method overloads for all the
permutations of the parameter types.  This leads to a massive increase in
methods but could provide better performance at run time; It may happen
already, or it certainly could in the future, that the DLR is able to
calculate the method required from the calling code (i.e. Ruby code) and
generate IL that will call that method directly during execution.  Therefore
the type lookup only needs to happen once.  This would make a huge
difference in some of the BigDecimal functionality where you may well be
doing complex calculations and expecting a reasonable level of performance.
The trouble with this is that it is a right pain to code up and leaves lots
of room for programmer error.  Also I imagine that this will lead to even
longer start-up times for IronRuby, which I suspect is going to be the major
performance issue going forward, what with all the code generation and JIT
compilation.

 

Any one got thoughts on this?

 

Pete

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