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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] Reopened: (MATH-349) Dangerous code in "PoissonDistributionImpl"
Date Tue, 09 Mar 2010 13:46:27 GMT

     [ https://issues.apache.org/jira/browse/MATH-349?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Phil Steitz reopened MATH-349:
------------------------------


Issue (2) in the bug description remains open.  I think we should leave this issue open until
we have a solution for this.  As stated above, I can see two ways to fix this:

a) modify the normal approximation implementation so that it does not change the parameters
of z
b) eliminate pluggability of z (i.e., deprecate and then remove the constructor that accepts
a normal instance as a parameter)

a) could be accomplished in 2.x, but it would complicate the code and could be bad for numerics.
 My vote is for b) - add a warning (about safety as well as deprecation), deprecate now and
if we get no complaints before 3.0, remove then.

> Dangerous code in "PoissonDistributionImpl"
> -------------------------------------------
>
>                 Key: MATH-349
>                 URL: https://issues.apache.org/jira/browse/MATH-349
>             Project: Commons Math
>          Issue Type: Bug
>            Reporter: Gilles
>            Priority: Minor
>
> In the following excerpt from class "PoissonDistributionImpl":
> {code:title=PoissonDistributionImpl.java|borderStyle=solid}
>     public PoissonDistributionImpl(double p, NormalDistribution z) {
>         super();
>         setNormal(z);
>         setMean(p);
>     }
> {code}
> (1) Overridable methods are called within the constructor.
> (2) The reference "z" is stored and modified within the class.
> I've encountered problem (1) in several classes while working on issue 348. In those
cases, in order to remove potential problems, I copied/pasted the body of the "setter" methods
inside the constructor but I think that a more elegant solution would be to remove the "setters"
altogether (i.e. make the classes immutable).
> Problem (2) can also create unexpected behaviour. Is it really necessary to pass the
"NormalDistribution" object; can't it be always created within the class?

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