Re: Dissasembly pre and post increments (was Re: How to instantaneously convert array of Integers into an array on int's?)

Joshua Cranmer <Pidgeot18@verizon.invalid>
Wed, 13 Aug 2008 23:45:16 -0400
rossum wrote:

On Wed, 13 Aug 2008 19:43:57 +0200, Andrea Francia

I don't know why it's good habit using the pre-increment, but this is
not the first time I have heard this thing.

To be succinct, I believe this dates from older compilers where a
post-increment operation was more expensive than pre-increment, but the
equivalence of the two (in any sane environment) means that modern
compilers should be able to optimize the two to the same thing in this

I code in C++ as well as Java, it is true in C++ because classes can
have their own pre- and post- increment operators.

I can make the && operator in C++ perform multidimensional matrix
inversion if I wish, but that operation will most likely confuse anyone
who uses it. Justifying a tradition on the basis of what a user *may*
do, especially if such actions require defying conventional logic.

 > I like to maintain

the habit whatever one of the C-style languages I am using. I agree
it is less important in Java where you cannot add operators to
classes. Think of the work needed to pre-increment or post-increment
a BigInteger.

I've not decided how I would like to see operator overloading
implemented in Java. Personally, I think an
interface+implementation+generics model works best (although getting an
int * BigInteger operator is not going to be intuitive), but the
annotation model also has its strong points.

In any case, based on some of my experiences in the GCC world, I think
using annotations to specify compiler hints would be useful here.
Hypothetically speaking:

interface Incrementor<T> {
    // ++obj -> obj.preIncrement();
    T preIncrement();
    // obj++ -> obj.postIncrement();
    // I'm not quite happy with this model
    T postIncrement();
public class BigInteger implements Incrementor<BigInteger> {
    public BigInteger preIncrement() {
      // increment self
      return this;
    public BigInteger postIncrement() {
      BigInteger ret = new BigInteger(this);
      // increment self
      return ret;

The annotation IfIgnored tells the compiler that if the return value is
ignored, the method is equivalent in function to preIncrement. Sure,
strong powers of abuse, but if operator overloading is implemented in
any case, there's already strong temptations for abuse anyways.

Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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