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Comment by almostgotcaught | Hacker News Reader

> Invariants are functions that run at the start and end of every public member function

these are just runtime assertions

EDIT: how am i getting downvoted for copy-pasting literally what the article verifies?

Yes, but they are guaranteed to run at the beginning and end. C/C++ asserts need to handle any return path, whereas D has functionality to mark statements to run at the end of any return path while only being written once.

See also the scope(exit) feature.

You can accomplish the same exact thing with

https://en.cppreference.com/w/cpp/experimental/scope_exit.ht...

The idea for scope-exit came from Andrei Alexandrescu. See https://dlang.org/articles/exception-safe.html

He demonstrated it with C++ templates, but the D one is far more straightforward.

Maybe it's the editorial "just"?

Like: software programs can't be that difficult to create properly because they are just 1s and 0s.

This is not the first time someone getting down-voted for using the word "just". I do not know if this really is warranted, however.

I think there's something to be said about them running automatically that is lost when you say they're just asserts.

i don't get it - if do

  int foo(int a) {
    assert(a > 5);
    int b = a * 10;
    assert(b > 50);
    return b;
  }

do you think those asserts don't "run automatically"?

You define the invariants once for the class and they are run around every public function. Done manually you'd probably use a helper object that calls the invariants in its constructor and destructor (have to handle exceptions) that you have to add to every public function's definition.

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