I don't mean a class variable. I want a variable that can be used everywhere. How should I initiate it?
I know one way is Smalltalk at: #variableName put: theValue. but I don't want to give it value as soon as I create it.
This should do the trick:
Smalltalk at: #VariableName put: nil
When you create a global variable in the Smalltalk dictionary, you are creating an Association which has a key and a value, so you can't get away without providing some sort of value.
You can come back later and change the value with:
Smalltalk at: #VariableName put: newValue
Any compiled code that references the global variable will see the new value, because the compiled code references the Association.
Related
Let's say I have a type of object in my game called oCharacter. All characters must have names, so I want to provide one when I construct the object. I can do that by using the _variables argument of instance_create_layer:
instance_create_layer(0, 0, "Instances", oCharacter, { name: "George" });
I could even make sure that I don't forget to do this by making a "constructor" function for characters and only instantiating them using that:
function character_create(_x, _y, _name) {
return instance_create_layer(_x, _y, "Instances", oCharacter, { name: _name });
}
But this approach has two problems.
The first is that I or another developer might forget about this convention and instantiate a character directly using instance_create_layer, forgetting to pass a name and setting up a runtime error further down the road.
The second (related) issue is that Feather doesn't know about this convention, so my Feather window is full of error messages about references to instance variables that aren't declared in the Create event - but I don't see how I can declare these variables in the Create event, as I'm expecting their value to be provided by the creator.
Is there some way of doing this that addresses these issues?
The first problem is just about setting rules about the code conventions within your team, if your team does not know about these conventions you want them to follow, then you should tell it them in a meeting.
For the second problem: Maybe you could create an empty/nullable variable in the Create Event? I'm afraid I'm not familiar with Feather
Personally I would do two things for this.
Create development standards for the team and put them in something like a Word document, wiki page, onenote, whatever makes the most sense for your team.
I would use a function to create the instance of the object (like you're doing there), and have some simple validation checks inside of the create event itself that will cancel it's creation (something like a guard clause) and output a debug message with a reminder.
It's not the most elegant solution but that should do the trick (assuming you haven't found something else by now haha)
For interfacing HDF5, I need to get a reference to/value of an external variable exported by the library, and pass it to other external functions.
For example, there is a variable representing the native double type: H5T_NATIVE_DOUBLE_g.
In VW, DLLCC, this is achievable thru a declarative annotation:
H5T_NATIVE_DOUBLE_g
<C: hid_t H5T_NATIVE_DOUBLE_g>
Is there anything similar in Squeak FFI? Is there any support for such use case?
After inquiry, there seem to be at least a basic support in the (Threaded)FFIPlugin:
ExternalAddress class>>loadSymbol: moduleSymbol module: module
<primitive: 'primitiveLoadSymbolFromModule' module: 'SqueakFFIPrims'>
^ self primitiveFailed
So we might create an ExternalData, get its address via above message (passing the global variable name and a given ExternalLibrary as module argument), and specify its type.
We can then use this ExternalData to pass the address if the external function expects a pointer.
To pass the value, one needs to dereference the address, not sure that it is automated by the plugin...
In my case, I know I will have to pass the value, so I may directly de-reference the address to get the value and store that (assuming that the global variable is assigned once at initialization and won't change afterward and assuming that initialization has already occured at library load time - lots of application specific assumptions...).
While modifying an existing program's CASE statement, I had to add a second block where some logic is repeated to set NetWeaver portal settings. This is done by setting values in a local variable, then assigning that variable to a Changing parameter. I copied over the code and did a Pretty Print, expecting to compiler to complain about the unknown variable. To my surprise however, this code actually compiles just fine:
CASE i_actionid.
WHEN 'DOMIGO'.
DATA: ls_portal_actions TYPE powl_follow_up_sty.
CLEAR ls_portal_actions.
ls_portal_actions-bo_system = 'SAP_ECC_Common'.
" [...]
c_portal_actions = ls_portal_actions.
WHEN 'EBELN'.
ls_portal_actions-bo_system = 'SAP_ECC_Common'.
" [...]
C_PORTAL_ACTIONS = ls_portal_actions.
ENDCASE.
As I have seen in every other programming language, the DATA: declaration in the first WHEN statement should be encapsulated and available only inside that switch block. Does SAP ignore this encapsulation to make that value available in the entire CASE statement? Is this documented anywhere?
Note that this code compiles just fine and double-clicking the local variable in the second switch takes me to the data declaration in the first. I have however not been able to test that this code executes properly as our testing environment is down.
In short you cannot do this. You will have the following scopes in an abap program within which to declare variables (from local to global):
Form routine: all variables between FORM and ENDFORM
Method: all variables between METHOD and ENDMETHOD
Class - all variables between CLASS and ENDCLASS but only in the CLASS DEFINITION section
Function module: all variables between FUNCTION and ENDFUNCTION
Program/global - anything not in one of the above is global in the current program including variables in PBO and PAI modules
Having the ability to define variables locally in a for loop or if is really useful but unfortunately not possible in ABAP. The closest you will come to publicly available documentation on this is on help.sap.com: Local Data in the Subroutine
As for the compile process do not assume that ABAP will optimize out any variables you do not use it won't, use the code inspector to find and remove them yourself. Since ABAP works the way it does I personally define all my variables at the start of a modularization unit and not inline with other code and have gone so far as to modify the pretty printer to move any inline definitions to the top of the current scope.
Your assumption that a CASE statement defines its own scope of variables in ABAP is simply wrong (and would be wrong for a number of other programming languages as well). It's a bad idea to litter your code with variable declarations because that makes it awfully hard to read and to maintain, but it is possible. The DATA statements - as well as many other declarative statements - are only evaluated at compile time and are completely ignored at runtime. You can find more information about the scopes in the online documentation.
The inline variable declarations are now possible with the newest version of SAP Netweaver. Here is the link to the documentation DATA - inline declaration. Here are also some guidelines of a good and bad usage of this new feature
Here is a quote from this site:
A declaration expression with the declaration operator DATA declares a variable var used as an operand in the current writer position. The declared variable is visible statically in the program from DATA(var) and is valid in the current context. The declaration is made when the program is compiled, regardless of whether the statement is actually executed.
Personally have not had time to check it out yet, because of lack of access to such system.
I have a pointer to an array or to a variable. I want to get the name of that array or variable. How to get this in LLVM?
I am trying to instrument a function to which an array or variable is passed through pointer. I want to get the name of that array or variable argument. I am instrumenting my functions using LLVM.
You need to use debug information for that, because otherwise names from the original C code do not get represented in LLVM IR, in the general case. See the debug info document. In particular, look in the sections about "#llvm.dbg.declare" and "Global Value Descriptors"
Can anyone tell me what the difference is between these 2 lines of code, which one is better to use?
System::String ^MyStr = gcnew System::String(MyStr);
System::String ^MyStr;
Those lines are not equivalent. In the first one, you will get an exception beacuse you're trying to create a String from an uninitialized tracking handle (MyStr). In the second one, MyStr is declared, not defined, it points to garbage and will throw an exception if you attempt to use it. Which one you should use depends on the rest of the code
The second one creates a new handle variable. If it's a local variable, then as #dario_ramos says, it's uninitialized, and your program will likely crash if you try to use the handle before assigning it. If it's a member variable or global, then it will be nullptr.
The first one is similar, although it can only be used for locals or globals (member variables use the ctor-initializer syntax in C++/CLI just like plain C++), and does exactly what you're not permitted to do. It reads the brand new uninitialized handle and passes it to the System::String constructor. If by chance the constructor finishes, a handle to the newly constructed String will be placed into the variable as part of initialization. But because the constructor is trying to make a copy of random garbage (if it's a local) or nullptr (if a global), most likely it will simply crash.
It's a bad idea to use the value of any variable in its own initializer (sometimes you need to use the address, never the value).