This is kind of a strange question. Basically there’s a const struct defined in a framework that I may or may not be able to load. Let’s say the struct is called “ExternalStruct”. I can tell whether or not I can load the framework but I can’t use the variable by name because if I can’t load the framework it will crash. How can I do what I’m trying to do (reference ExternalStruct but only if I can load this framework)?
Thanks
EDIT:
My other thought was to use an ifdef but I’m not sure how those work with respect to compile time vs link time.
If you can get the CFBundle/NSBundle for the library in question, once it's loaded you can use CFBundleGetDataPointerForName.
Related
What is a "suitable guard" and what does it look like?
Linked this question because it refers to the same compiler message and the answer mentions a guard but not how to create one. Looked through the AspectJ docs but did not find and answer there.
This Lint warning is usually switched off in AJDT (AspectJ Development Tools) within Eclipse, but you can activate it as a warning or even error like this (I had to do it to actually see it at all when trying to reproduce your issue):
You can just ignore the Lint warning because basically it only says that there is no way for certain pointcuts to populate the thisJoinPoint object lazily during runtime because the pointcut has no dynamic component like if(), cflow() or similar, which is actually good news because it means that all your joinpoints can be determined statically during compile/weave time and are thus faster than dynamic pointcuts. On the other hand, the warning says that the tjp object always has to be created because for some reason it is also always needed during runtime and thus cannot be instantiated lazily.
I'm creating an application in VBA that uses a reference from vbscript.dll
I'm trying to figure out the best way to load the library, and am having difficulty distinguishing between using a declare function (http://msdn.microsoft.com/en-us/library/aa716201(v=vs.60).aspx) or just dynamically adding it to the list of references (How to add a reference programmatically, part 2 of the top answer)
If anyone can clarify the difference in result between the two, and maybe some advantages of one, I would be very happy.
My Notes:
I like the looks of a simple declare function, for one thing it's short and looks nice. For another, I like avoiding hard coded paths unless I know the files won't be found in different places.
On the other hand, I really like the error handling in method 2.
Declare is (typically) used for calling stdcall-supported functions exported from Windows DLLs. The VB run-time takes care of calling LoadLibrary, GetProcAddress, etc. to locate and load the functions you've declared. Most of the Windows API is used this way from VB/VBA.
References are used for COM objects -- that is, libraries that define a type library and a COM interface.
It's rare for a library to support both. If what you have is a COM library (if it appears in the 'References' dialog), add a reference to it and instantiate it that way.
I'm aware this might be a broad question (there's no specific code for you to look at), but I'm hoping I'd get some insights as to what to do, or how to approach the problem.
To keep things simple, suppose the compiler that I'm writing performs these three steps:
parse (and bind all variables)
typecheck
codegen
Also the language that I'm building the compiler for wants to support late-analysis/late-binding (ie., it has a function that takes a String, which is to be compiled and executed as a piece of source-code during runtime).
Now during parse-phase, I have a piece of context that I need to keep around till run-time for the sole benefit of the aforementioned function (because it needs to parse and typecheck its argument in that context).
So the question, how should I do this? What do other compilers do?
Should I just serialise the context object to disk (codegen for it) and resurrect it during run-time or something?
Thanks
Yes, you'll need to emit the type information (or other context, you weren't very specific) in your object/executable files, so that your eval can read it at runtime. You might look at Java's .class file format for inspiration; Java doesn't have eval as such, but you can dynamically spin new bytecode at runtime that must be linked in a type-safe manner. David Conrad's comment is spot-on: this information can also be used to implement reflection, if your language has such a feature.
That's as much as I can help you without more specifics.
My XCode project has grown somewhat, and I know that there are class files in there which are no longer being used. Is there an easy way to find all of these and remove them?
If the class files just sit in your project without being part of a target, just click on the project itself in the tree view, so you see all files in the table. Make sure you see the "Target" column in the table view, iterate through your targets and find the files that don't have a check anywhere -> they are no longer compiled.
But if you still compile the classes and they are no longer used, that case is a bit more difficult. Check out this project
http://www.karppinen.fi/analysistool/#dependency-graphs
You could create a dependency graph and try to find orphaned classes that way.
Edit: Link went dead, but there still seem to be projects of Objective-C dependency graphs around, for example https://github.com/nst/objc_dep
if they are C or C++ symbols, then you can just let the linker do the work for you.
if you're looking to remove objc symbols, then try to refactor the class name (e.g. to rename the class), and preview the dependencies that it turns up. if you reference classes/selectors/etc. by strings then... it may not be so effective. unfortunately, you often have to also test manually, to verify that removing a class does not break anything. remember that resources (like xibs) may reference/load objc classes as well.
This is a tricky question due to how dynamic objective-c is as you can never guarantee that a class is not going to be used.
Consider if you generate a class name and a selector at run time and then look up that class, instantiate that class and then call a method on that newly created object using that newly created selector. No where in your code do you explicitly name and instantiate that object but you are able to use it anyways. You could get that class name and selector name from anywhere outside of your code, even from some data from a server some where. How would you ever know which class is not going to be used? Because of this there are no tools that are able to perform what you are requesting.
Searching the project with the class name might be an option, thought it may not be the best solution. Specially it might be time consuming when you have many classes.
Ok, well I have sorta of an odd situation. I have a two applications. One is the main application and the other is a helper bundle that is loaded during run time. What I want to do is to call a function defined within the main application from the bundle so that code does not have to be copied over. I have tried setting the header declaration for the function
NSString *TXReadableTime(NSTimeInterval date, BOOL longFormat);
within the helper bundle, but it still fails to compile. This is because one of my selectors is calling the function and the compiler is not finding it within the code. Only the header reference.
So I guess what my real question is, is there a way to have dynamic functions? One that is promised to the compiler, but is handled by a separate process. The helper bundle itself is allocated into memory so it has access to selectors of the main application, but I do not want to rewrite the function into a selector because it would require a lot of work.
Use -bundle_loader linker flag to specify the executable which will load the plugin. See ld man page, another Apple doc, and this informative blog post.