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Haskell typeclasses often come with laws; for instance, instances of Monoid are expected to observe that x <> mempty = mempty <> x = x.

Typeclass laws are often written with single-equals (=) rather than double-equals (==). This suggests that the notion of equality used in typeclass laws is something other than that of Eq (which makes sense, since Eq is not a superclass of Monoid)

Searching around, I was unable to find any authoritative statement on the meaning of = in typeclass laws. For instance:

• The Haskell 2010 report does not even contain the word "law" in it
• Speaking with other Haskell users, most people seem to believe that = usually means extensional equality or substitution but is fundamentally context-dependent. Nobody provided any authoritative source for this claim.
• The Haskell wiki article on monad laws states that = is extensional, but, again, fails to provide a source, and I wasn't able to track down any way to contact the author of the relevant edit.

The question, then: Is there any authoritative source on or standard for the semantics for = in typeclass laws? If so, what is it? Additionally, are there examples where the intended meaning of = is particularly exotic?

(As a side note, treating = extensionally can get tricky. For instance, there is a Monoid (IO a) instance, but it's not really clear what extensional equality of IO values looks like.)

With regard to the Log4j JNDI remote code execution vulnerability that has been identified CVE-2021-44228 - (also see references) - I wondered if Log4j-v1.2 is also impacted, but the closest I got from source code review is the JMS-Appender.

The question is, while the posts on the Internet indicate that Log4j 1.2 is also vulnerable, I am not able to find the relevant source code for it.

Am I missing something that others have identified?

Log4j 1.2 appears to have a vulnerability in the socket-server class, but my understanding is that it needs to be enabled in the first place for it to be applicable and hence is not a passive threat unlike the JNDI-lookup vulnerability which the one identified appears to be.

Is my understanding - that Log4j v1.2 - is not vulnerable to the jndi-remote-code execution bug correct?

• Apache Log4j Security Vulnerabilities

• Zero-day in ubiquitous Log4j tool poses a grave threat to the Internet

• Worst Apache Log4j RCE Zero day Dropped on Internet

• ‘Log4Shell’ vulnerability poses critical threat to applications using ‘ubiquitous’ Java logging package Apache Log4j

This blog post from Cloudflare also indicates the same point as from AKX....that it was introduced from Log4j 2!

Update #1 - A fork of the (now-retired) apache-log4j-1.2.x with patch fixes for few vulnerabilities identified in the older library is now available (from the original log4j author). The site is https://reload4j.qos.ch/. As of 21-Jan-2022 version 1.2.18.2 has been released. Vulnerabilities addressed to date include those pertaining to JMSAppender, SocketServer and Chainsaw vulnerabilities. Note that I am simply relaying this information. Have not verified the fixes from my end. Please refer the link for additional details.

Is there any practical difference between std::array and const std::array?

It looks that non-const array holding const elements is still not able to be swapped; assignment operator is not working either.

When should I prefer one over the other one?

Trying to install openssl on homebrew using:

I am trying to efficiently compute a summation of a summation in Python:

WolframAlpha is able to compute it too a high n value: sum of sum.

I have two approaches: a for loop method and an np.sum method. I thought the np.sum approach would be faster. However, they are the same until a large n, after which the np.sum has overflow errors and gives the wrong result.

I am trying to find the fastest way to compute this sum.

I'd like to abstract some of my GitHub Actions with a reusable workflow.

In order to do this, I need to call my newly defined callable workflow in the format {owner}/{repo}/{path}/{filename}@{ref}

e.g. (from the docs)

Suppose I have a simple Duration class:

I have a small loop of code which is throwing Uncaught RangeError: Invalid Array Length

I was able to reproduce it with just this in the Google Chrome console

I am working on a "heartbeat" application that pings hundreds of IP addresses every minute via a loop. The IP addresses are stored in a list of a class Machines. I have a loop that creates a Task (where MachinePingResults is basically a Tuple of an IP and online status) for each IP and calls a ping function using System.Net.NetworkInformation.

The issue I'm having is that after hours (or days) of running, one of the loops of the main program fails to finish the Tasks which is leading to a memory leak. I cannot determine why my Tasks are not finishing (if I look in the Task list during runtime after a few days of running, there are hundreds of tasks that appear as "awaiting"). Most of the time all the tasks finish and are disposed; it is just randomly that they don't finish. For example, the past 24 hours had one issue at about 12 hours in with 148 awaiting tasks that never finished. Due to the nature of not being able to see why the Ping is hanging (since it's internal to .NET), I haven't been able to replicate the issue to debug.

(It appears that the Ping call in .NET can hang and the built-in timeout fail if there is a DNS issue, which is why I built an additional timeout in)

I have a way to cancel the main loop if the pings don't return within 15 seconds using Task.Delay and a CancellationToken. Then in each Ping function I have a Delay in case the Ping call itself hangs that forces the function to complete. Also note I am only pinging IPv4; there is no IPv6 or URL.

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