I've been stuck on this for a while now. I am trying to send the following:
boost::shared_ptr<uint8_t[]> m_data
over the wire using:
_socket.async_send_to(boost::asio::buffer(m_data), m_remote_endpoint,
boost::bind(&UDPServer::handle_send, this, message,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
I get the error "no instance of overloaded function boost::asio::buffer matches the argument list boost::shared_ptr<uint8_t[]>"
m_data is filled in another function.
I suspect this is because I actually have to use the key word new on m_data. But I can't quite figure out how to do it. I've tried a few different variations. Can anybody offer me some insight here? This is probably more a question of how to dereference a shared pointer then anything. Thanks in advance!
boost::asio::buffer has an impressive lists of consttructors, but neither of them takes shared_ptr<[]> (possibly an oversight form lib authors).
In your case, you simply need to derefence shared ptr, for example, by calling get on it.
Related
What does = do here?
List<Segment> totalSegments = flight.departureFlight.segments;
Do both, totalSegments and flight.departureFlight.segments point to the same memory reference or totalSegments has the same data as flight.departureFlight.segments but points to a different memory location?
My understanding was that the latter should happen since dart is pass by value and not reference. However, a very annoying bug occurred when I added this line below that one:
totalSegments.addAll(flight.returnFlight.segments);
This above line actually modified the flight variable which in turn somehow modified the AsyncSnapshot from the StreamBuilder. Although, I wasn't using the variable anywhere else and not modifying other variables mentioned.
This all happened inside build function of a Stateless Widget. Maybe that has to do something with it.
I tried reading dart documentation for it, but either I couldn't find what I am looking for or the information is simply missing there. Read this too, but according to this, my use case shouldn't happen.
When it comes to objects as in your case, you are assigning a reference to an existing object (memory location) to a new variable. While acting upon that reference, you change the same object.
If this is not what you intend, check out answers related to (deep) copying of the objects
You were mistaken by the fact that Dart passes by value, and not by reference. Actually, it is exactly the opposite: (Almost) everything is always passed by reference (Which is usually a good thing!) Therefore, it is quite logical that because you edited totalSegments your departureflight.segments got edited too. It is a synonym. One of the ways to solve your problem would be:
List<Segment> totalSegments = List();
totalSegments.addAll(flight.departureFlight.segments.toList());
List<Segment> totalSegments = flight.departureFlight.segments;
This expression does the following.
Assigns the value of the expression flight.departureFlight.segments to variable totalSegments.
This and only this and nothing more.
There is no need to know what is really happening, because this is what happens.
P.S.
What value will be obtained as a result of executing the expression flight.departureFlight.segments is another question, because it depends on the implementation of the members of the operands of the expression flight.departureFlight.segments.
Occasionally, I find myself in situations where it would be useful to do something like this:
HTML::FormHandler::Field::Text->new(
name=>'name',
label=>'Name',
value=>'Ryan'
)->render();
There's nothing in the docs I've found that indicate that this shouldn't work. But apparently it doesn't because I get an error saying that the render routine doesn't exist in HTML::FormHandler::Field::Text.
Maybe I'm misunderstanding how widgets get applied and rendered, but I sure wish this or some alternative worked! Sometimes, it doesn't make sense to build up a whole "form" just for one field. Any thoughts?
It is called chaining. It is only going to work if method returns $self.
An article about this: http://www.perlmonks.org/?node_id=448444
Regards,
This is maybe a more cosmetic problem, but I find it really annoying as I always end up with some ugly code. And readability is always important, right?
I want to check if a value exists in a hash within a hash. So what I do is this.
already_exists_data[:data][:user_id]
But that can get me a nullpointer exception if :data is nil and checking :data might give me a nullpointer if already_exists_data is nil. So what I end up with is this:
if already_exists_data && already_exists_data[:data] && already_exists_data[:data][:user_id]
# Do stuff
end
Now that's some nasty looking code. Perhaps I should modify the hash to be an object instead. But I keep bumping in to this problem sometimes and was wondering how you guys confront it.
I'm currently coding in Ruby but I've had this problem with multiple other languages.
If I ask my butler to pick up the box of chocolates on the dining room table in Victoria street 34, I ask him just that. I don't want to say: Go find Victoria Street, and, if you find it, please look for number 34, and if you find it ...
I can do that because he catches his own errors: if he doesn't find the street he will just return empty-handed.
So you should use a try with an empty exception handler. In pseudo-code:
try {chocolates = streets("Victoria")(34)("dining room")("table")}
In languages (like ruby, with some homespun syntactic sugar) where blocks are expressions you might write:
if try {already_exists_data(data)(user_id)}
do_stuff
The language itself can also help: in perl, $streets{Victoria}[34]{dining_room}{table} is undefined when e.g. $streets is. Of course, your butler may come home empty-handed for years before you discover that the address is wrong. The try block solution - and your if .. && .... - have the same drawback: only use them when you really don't care if Victoria Street has a number 34 or not.
Language-agnostic solution: do not use nulls. Ever. Enforce this rule across your projects. If you absolutely have to, wrap them into Either/Optional which adds explicitness. Some languages, such as Scala, have the notion of Optional already built in.
Java-specific solution: if you have to use nulls, annotate method arguments and return values with #Nullable and #Nonnull. Decent IDEs (such as IntelliJ) are capable of analysing your code and highlighting possible null dereferences, if a value is acquired from such a method.
Another possibility is to wrap the hash access with a function call, and do the "dirty" work within the function. Then your code will be something like (pseudo-code syntax):
accessHash(already_exists_data, data, userid)
Note: you can get fancy with accessing nested hashes based on the number of parameters passed to the wrapper function, so it works in a multiple of situations.
I'm looking for a Perl module that is a port of this where I can basically create an object, call a tokenize() subroutine, pass in a pile of text and get back a list of tokens. Something to that effect. If it doesn't exist I'll do it, but no sense in reinventing the wheel, right? :) TIA.
I couldn't find an exact match, but could one of Lingua::EN::Tagger, Lingua::Treebank, Text::StemTagPOS, Lingua::Stem::Snowball or Treex::EN handle the problem?
I'm working on a Perl module and whenever I call the skip() method I wrote in the following way:
$cursor->skip(4);
I get:
Undefined subroutine &MyModule::Cursor::skip called at t/tester.pl line 24.
(in cleanup) invalid object at t/tester.pl line 24.
When I call it like:
MyModule::Cursor::skip($cursor, 4);
Perl finds it!
Oddly, if I name "skip" anything else ("skipper", "hello"), this syntax works:
$cursor->skipper(4);
I thought maybe skip() was a "secret" reserved key word or something, but I've also got methods named sort() and next() (which I know are reserved), and those work fine.
I'd really like to name this method "skip." Does anyone know why Perl can't find it?
skip() is exported from Test::More, which you might have loaded since your executable is named t/tester.pl.
What does ref($cursor) yield you? It should be a blessed MyModule::Cursor object, but the "invalid object" error might be suggesting the object was not constructed properly.
EDIT: perldiag gives another clue: "in cleanup" signifies that a problem was encountered by the object's destructor. Assuming you don't already have a destructor in the object, create a MyModule::Cursor::DESTROY method that Data::Dumps the object to see what it looks like at this time.
A concise snippet of example code that exhibits this behaviour would be very helpful.
Without actual code, it's difficult to debug this.
Do you use MyModule::Cursor in your test code? When you replaced skip with skipper, were you calling it in exactly the same way from your test module? Are you able to use skip from a throw-away (one-liner or very short script)?
Where I'm going with this is looking for an error in your test code, rather than the module.
UPDATE: You're not doing something like declaring methods on MyModule::Cursor in two different files, are you? The error message you're getting tells me it has a blessed reference to an object of type MyModule::Cursor, so it knows about the class; but then it can't find the definition of skip. Do you happen to declare part of MyModule::Cursor in one file, and skip in another, and your test module isn't including the second file? Or do you have a syntax error somewhere around your definition of skip -- a missing semi-colon or unpaired curly brace? (But then again, why would MyModule::Cursor::skip work where $cursor->skip does not?)