Dependent instances in one list - instance

Question

I have a problem in code design. I try to read some files and create for every file one or more instances (dependin on the content). But some instances depend on other files in the list, so that every instance has to know the top class. Following example should illustrate what I mean:
class SetOfAll(object)
def __init__(self):
self.matrjoschkas = []
def add(self, matrjoschka):
self.matrjoschkas.append(matrjoschka)
def create_matrjoschkas(self):
for file in glob.glob('*.txt'):
self.add(Matrjoschka(file, self))
class Matrjoschka(object)
def __init__(self, file, container):
self._container = container
...
if some condition:
self._container.add(Matrjoschka(..., self._container))
Is there an elegant way to avoid, that every instance has to know the top class? Because in my case it's a little bit more complicated and it would be good if some factory could do it.

Answer 1

Well, there are certainly many ways of doing this, but from what I can see you just need a way to explicitly state the dependencies between files. You could then ask a factory to create a list of files based on the file's source and the configured dependencies.
Pseudo-code:
filesFactory = new FilesFactory({
file1: ['file2', 'file3'] //file1 depends on file2 and file3
});
filesSource = new GlobFilesSource('*.txt'); //FilesSource could be an abstraction and GlobFilesSource a concrete implementation
allFiles = filesFactory.resolveAllFilesFrom(filesSource); // ['file1', 'file2', 'file3']
If the dependency conditions are more complex than a simple id matching then you could just configure predicates. Here's a pseudo-code sample using a predicate to achieve the same dependency configuration as above:
[
{
predicate: function (currentFiles) {
return currentFiles.contains('file1');
},
files: ['file2', 'file3']
}
]
This design is much more flexible than yours because not only the Matrjoschka class doesn't have to know about it's container, but it also doesn't have to know about dependency rules.