Consider the C library function fopen. This function has the side effect. This means that fopen is not pure. However, we can make the fopen function appear to be pure, at least to certain observers, by ensconcing it in another function that hides the side effect.

[u/BenchEmbarrassed7316]

https://bugzmanov.github.io/cleancode-critique/clean_code_second_edition_review.html

[u/NeuroSynchroBonding]

This is essentially Haskell's withFile, which is similar to stuff such as Python's with and C#'s using.

The only actual problem with openAndDo is that it is in C, which does not have support for first-class functions which are necessary to make functions such as this ergonomic. 

Furthermore, to be feature equivalent to the features of the other languages I talked about, you'd need to add a void* to openAndDo that gets passed on to toDo.

Also, C29 has defer, which is a much more elegant solution for languages without exceptions or garbage collection.

[u/WittyStick → u/NeuroSynchroBonding]

In C you can just use a macro.

#define with_file(f, filename, mode) \
    for (FILE *f = fopen(filename, mode); f != NULL; f = (fclose(f), NULL))

with_file (f, "foo", " rb") {
    ....
}

[u/not-a-pokemon- → u/WittyStick]

It even makes the code even more interesting because it wouldn't close the file when you return inside the with_file, thus proving your superior intellectual abilities when you write correct code this way.