Chris Angelico <ros...@gmail.com>:
> On Wed, Mar 5, 2014 at 6:49 AM, Marko Rauhamaa <ma...@pacujo.net> wrote:
>> public ConnectionPool(int maxConnections, String url) throws SQLException {
>> try {
>> super(() -> {
>> try {
>> return DriverManager.getConnection(url);
>> } catch ( SQLException ex ) {
>> throw new WrappedSqlException(ex);
>> }
>> }, maxConnections);
>> } catch (WrappedSqlException wse) {
>> throw wse.getSqlException();
>> }
>> }
>>
>> ===JAVA END=============================================================
>
> You're not doing the same thing, though. The Java rigmarole is to
> ensure that an SQLException thrown in getConnection will propagate up,
> despite (presumably) something inside the equivalent of
> super().__init__ that swallows SQLExceptions. Of course it looks
> tidier when you don't do the messy bit.
See <URL: http://stackoverflow.com/questions/14039995/
java-8-mandatory-checked-exceptions-handling-in-lambd
a-expressions-for-standard>.
The "rigmarole" is trying to get around Java's mandatory exception
handling limitations, which Python doesn't have.
You are not allowed to pass a lambda to the super constructor that
throws an SQLException. To get around the limitation, a RuntimeException
wrapper is created to smuggle the SQLException through the compiler's
defenses. Any code is free to throw a RuntimeException.
I don't know, though, if this is that good of an example. I don't know
if the lambda gets called within the constructor or, as I would guess,
whenever a new connection is needed. The whole wrapping exercise would
be for nothing, then.
Here's a more prosaic example (probably contains errors):
===JAVA BEGIN===========================================================
private Map<TaxpayerIdNumber, Map<FormId, Form>> filings =
new TreeMap<TaxpayerIdNumber, Map<FormId, Form>>();
class FormFiling {
public FormFiling(TaxpayerIdNumber taxpayerId, Form form) {
this.taxpayerId = taxpayerId;
this.form = form;
}
public TaxpayerIdNumber getTaxpayerId() { return taxpayerId; }
public Form getForm() { return form; }
private TaxpayerIdNumber taxpayerId;
private Form form;
};
List<FormFiling> getForms(FormId formId)
{
List<FormFiling> forms = new LinkedList<FormFiling>();
for (Map.Entry<TaxpayerIdNumber, Map<FormId, Form>> payerEntry :
filings.entrySet()) {
TaxpayerIdNumber taxpayerId = payerEntry.getKey();
Map<FormId, Form> filing = payerEntry.getValue();
if (filing.containsKey(formId))
forms.add(new FormFiling(taxpayerId, filing.get(formId)))
}
return forms;
}
===JAVA END=============================================================
===PYTHON BEGIN=========================================================
filings = {}
def getForms(formId):
forms = []
for taxpayerId, filing in filings.iteritems():
if formId in filing:
forms.append((taxpayerId, filing[formId]))
return forms
===PYTHON END===========================================================
or:
===PYTHON BEGIN=========================================================
filings = {}
def getForms(formId):
return ((taxpayerId, filing[formId])
for (taxpayerId, filing) in filings.iteritems()
if formId in filing)
===PYTHON END===========================================================
Marko
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