I'm trying to factor out my increasingly big single CoffeeScript file in my Meteor project, and have followed the official advice on scoping global variables using this. However, even something simple like:
console.log("this=" + this)
#gave =
Transactions: new Meteor.Collection("Transactions")
Causes: new Meteor.Collection("Causes")
Generates terminal errors and the server won't start:
=> Meteor server restarted
this=undefined
/home/g/workspace/gave/.meteor/local/build/server/server.js:321
}).run();
^
TypeError: Cannot set property 'gave' of undefined
at app/gave.coffee.js:6:11
According to the advice linked above,
Global variables can be set in CoffeeScript by using this (or CoffeeScript's # shorthand), because at the top level this refers to the global namespace (window on the client and global on the server).
So, I can't really figure out where I'm going wrong. Can you? :)
See ES5 - 15.3.4.4.
NOTE The thisArg value is passed without modification as the this
value. This is a change from Edition 3, where a undefined or null
thisArg is replaced with the global object and ToObject is applied to
all other values and that result is passed as the this value.
So, with the "use strict", meteor's .call(null) will effectively give you a this == null =).
Related
I am working on a project that deals with lots of atomic operations. Till now I didn’t knew about atomic_load() and was only relying on assignment operator to get value of an atomic type and I haven’t seen an error except of so much of testing. Those atomic types are changed by multiple processes and threads as well by atomic_compare_exchange_strong_explicit(), so they will need an old value every time, and that’s where I always did oldValue = <Atomic_ type_variable> and it always works fine.
Is that just by chance? Should I prefer using atomic_load()?
foo = atomic_var is just a shortcut syntax for foo = atomic_load(&atomic_var);
Which itself is a shortcut for foo = atomic_load_explicit(&atomic_var, memory_order_seq_cst); That has a use-case when you want to use an ordering weaker than the default seq_cst.
The main reason for using atomic_load explicitly in your source code is probably to remind human readers that a variable or pointer is atomic. Or maybe as a part of a macro, using atomic_load(&(macro_input)) would create a compile-time error for a non-atomic pointer.
As a "generic" function, you can't take a normal function-pointer to it.
Its existence may be just to make it easier to write the language standard, and explain everything in terms of functions.
It's not the actual assignment that's key here, it's evaluating the atomic variable in an rvalue context (reading it's value as part of an expression, like you typically find on the right-hand side of an =). printf("%d\n", my_atomic_var); is also equivalent to atomic_load.
And BTW, the same thing holds for atomic_var = foo; being exactly the same as atomic_store_explicit with mo_seq_cst. Here it is assignment that's key.
Other kinds of lvalue references to an atomic variable are different, like read-modify-write atomic_var++ is equivalent to atomic_fetch_add.
I'm playing around with Coffeescript, trying to convert a JavaScript file to Coffeescript. This is valid JavaScript:
element(by.model('query.address')).sendKeys('947');
This is invalid Coffeescript:
element(by.model('query.address')).sendKeys('947')
What is invalid about the Coffeescript? Coffeelint says "unexpected BY".
CoffeeScript uses the by keyword to let you use a specific step when looping through a range.
From the documentation:
To step through a range comprehension in fixed-size chunks, use by, for example:
evens = (x for x in [0..10] by 2)
Since JavaScript doesn't use by it's valid. For CoffeeScript, try renaming the by to something else.
In response to the comment, since Protractor provides its own by global variable, one idea is to alias it via CoffeeScript's embedded JavaScript syntax (code surrounded by back-ticks), then continue using CoffeeScript and the alias throughout your code.
You'll need to test this type of code:
ptorBy = `by`
element(ptorBy.model('query.address')).sendKeys('947')
Where ptor is just my short-hand for "Protractor." This translates to the following JavaScript:
var ptorBy;
ptorBy = by;
element(ptorBy.model('query.address')).sendKeys('947');
Python allows hash values only for immutable objects. For example,
hash((1,2,3))
works, but
hash([1,2,3])
raises a TypeError: unhashable type: 'list'. See the Python documentation. However, when I wrap a C++ class in Boost.Python via the usual boost::python::class_<> function, every generated Python class has a default hash function, where the hash value is related to the object's location in memory. (On my 64-bit OS, the hash value is the location divided by 8.)
When I expose a class to Python whose members can be changed (any mutable data structure, so this is a very common situation!), I do not want a default hash function but want a call to hash() raise the same TypeError as users receive for Python's own mutable data types. In particular, users shouldn't be able to accidentally use mutable objects as dictionary keys. How can I achieve this in the C++ code?
I found out how it goes:
boost::python::class_<MyClass>("MyClass")
.setattr("__hash__", boost::python::object());
A boost::python::object which is initialized with no arguments corresponds to None. The procedure for disabling hash generation in the pure Python C API is a little more complicated, as is described in the Python documentation. However, the above code snippet apparently does the job in boost::python.
On a sidenote: The Boost.Python behaviour mirrors the default behaviour of classes in Python, where objects are basically hashable as of object id (derived from id(x)):
>>> hash(object())
8795488122377
>>> class MyClass(object): pass
...
>>> hash(MyClass)
878579
>>> hash(MyClass())
8795488082665
>>>
I started using smalltalk and I am trying to add a new assignment operator :>.
The current operator used in pharo is no selector so I started to look into the class Scanner where the underscore _ can be enabled for assignments. I've tried to do it in a similar way but it did not work.
Do you have any idea or suggestion about how I achieve that?
For a start, have a look at the Method Scanner>>#xColon. This method is called whenever a colon is encountered in the input. By adding the following snippet to the top of the method, you can make it detect your new assignment token :>:
aheadChar = $> ifTrue: [
self step.
tokenType := #leftArrow.
self step.
^ token := #':=' ]
Like this :> behaves exactly like the normal assignment. By customising tokenType and token you can pass your new assignment operator to the parser (see Parser>>#expression and Parser>>#assignment:) and build a different AST (i.e. to achieve a different execution behaviour).
If you are interested in more flexibility you might want to look at Helvetia. Helvetia is a language workbench for Pharo that allows you to modify the host language and adapt the tools in a more modular fashion. One of the examples included with the distribution (CUSwapExample) is adding two new assignment operators to Smalltalk.
I'm writing simple chat program in Ada, and I'm having problem with chat window simulation - on button clicked it reads text form entry and puts it on text_view. Here is the code I've written and here is the compile output:
gnatmake client `gtkada-config`
gcc -c -I/usr/include/gtkada client_pkg.adb
client_pkg.adb:14:19: no candidate interpretations match the actuals:
client_pkg.adb:14:37: expected private type "Gtk_Text_Iter" defined at gtk-text_iter.ads:48
client_pkg.adb:14:37: found type "Gtk_Text_View" defined at gtk-text_view.ads:58
client_pkg.adb:14:37: ==> in call to "Get_Buffer" at gtk-text_buffer.ads:568
client_pkg.adb:14:37: ==> in call to "Get_Buffer" at gtk-text_buffer.ads:407
client_pkg.adb:15:34: no candidate interpretations match the actuals:
client_pkg.adb:15:34: missing argument for parameter "Start" in call to "Get_Text" declared at gtk-text_buffer.ads:283
client_pkg.adb:15:34: missing argument for parameter "Start" in call to "Get_Text" declared at gtk-text_buffer.ads:270
gnatmake: "client_pkg.adb" compilation error
Can anyone tell me what is the problem, since I have no idea why procedure Get_Buffer expects Gtk_Text_Iter, and why Get_Text miss Start parameter?
You have to call the correct procedures/functions.
In your example, you call Gtk.Text_Buffer.Get_Buffer, not the correct Gtk.Text_View.Get_Buffer. This is because you with and use Gtk.Text_Buffer, but don't use Gtk.Text_View. You should be careful what you use. Same for Get_Text.
If you add use clauses for Gtk.Text_View and Gtk.GEntry, those errors should disappear.
But I give you an advice: try to use as few as possible use clauses. That way you always know what function is really called.
TLDR: Add use Gtk.Text_View; use Gtk.GEntry; to the declaration part of the On_Btn_Send_Clicked procedure.