interpose | Function interposition for Linux and Mac OS

println always returns nil. You can get what you want by using with-out-str as follows:

You say a.dylib depends on b.dylib but b.dylib does not depend on a.dylib and that you want no calls in b.dylib to ever be interposed. You gave open as an example of an interposed function.

The example I gave was that a.dylib needs to call processFile that is defined in b.dylib and it opens files. You don't want the open call in b.dylib to be interposed ever (whether a.dylib is loaded or not).

The only way I know to pull this off is for processFile to dynamically load the C library instead of letting ld do it automatically.

There are two problems with this approach. The first is that each function that needs to call open will need one additional if statement to execute the code to resolve the symbol.

The other is that you need to know ahead of time the filename of the C library to load. And if there's a problem resolving the symbol, then you have to deal with a situation that most programs don't have to deal with; at least at a later time.

The code will look something like this:

IIUC

You were on the right track with your first try. You really have to override the attributes in the interface, but it doesn't have to be done in the constructor. You can do it in the class body and that way you can add a default value for them (not only can, but you must). If you make that class open you can then extend from it in all your classes.

What type of object are contexts, and how can a javascript method tell one apart from other javascript objects by inspecting its properties at runtime?

There is no special type. Every object can become a context by calling a method upon it. Most objects that will become a context of a method call do have that very method as an (inherited) property, but there's no guarantee.

You cannot tell them apart.

What are the semantics of context binding in javascript that would cause binding to a Proxy(context) to fail with an illegal invocation?

When the method is a native one. In user code functions, the this context being a proxy doesn't make a difference, when you access it then it will just behave as a proxy.

The problem is native methods that expect their this argument to be a native object of the respective type. Sure, those objects are still javascript objects, but they may contain private data on internal properties as well. A proxy's target and handler references are implemented through such internal properties as well, for example - you can sometimes inspect them in the debugger. The native methods don't know to unwrap a proxy and use its target instead, they just look at the object and notice that it doesn't have the required internal properties for the method to do its job. You could've passed a plain {} as well.

Examples for such methods can be found as builtins of the ECMAScript runtime:

• Map.prototype.has/get/set/…
• Set.prototype.has/get/set/…
• TypeArrayPrototype.slice/copyWithin/map/forEach/…
• Number/String/Boolean prototype methods

But also (and even more of them) as host objects supplied by the environment:

• window.alert/prompt
• EventTarget.prototype.addEventListener/removeEventListener
• document.createElement
• Element.prototype.appendChild/remove/…
• really just anything that's browser-specific
• but also in other environments, like the nodejs os module

I have tried unwrapping Proxies in the right places by coding in edge cases and by blanket/heuristic policies.

I think the only reasonable approach would be to check whether the called function is a native one, and unwrap all arguments (including the this argument) for them.

Only a few native functions could be whitelisted, such as most of those on the Array.prototype which are explicitly specified in the language standard to work on arbitrary objects.

The short answer is that you can't do it the way you want, i.e., through fixtures: https://github.com/pytest-dev/pytest/issues/2155. Basically, the number of things yielded or returned has to be known up front for pytest to properly compute the fixture and test dependency graph.

It appears that the only way is to fix the list elements before passing them to any of pytests's decorators. Here is an example, related to your other question, showing that the problem can not be solved by say a generator:

If we wish to do this task with a regular expression, we might want to start with an expression that passes newlines, similar to these:

For first question, i am doing same thing, i didn't get any error, please share your error.

Note: I will give you example using functional API, which gives little more freedom(personal opinion)

If I understand correctly, you want all calls to sub (or rather _Z3subP7AStructii) to actually be calling your _sub function instead? The problem is that when the "client" calls some_astruct->sub(...) it doesn't actually call _Z3subP7AStructii directly, and therefore your _sub function won't be called.

In other words, the "client" doesn't have a call to _Z3subP7AStructii, but instead it have a call to whatever some_astruct->sub is pointing to. The _Z3subP7AStructii function could even not be exported by the libA library (i.e. have internal linkage with e.g. static), and it could still be called through the structure.

A possible solution to this is not to "interpose" the sub function, but instead the AStruct_create function. In your version call the original, then replace the pointer to the sub function in the structure to your own function (possibly saving the original so you can use it).