take(1) can be dangerous

When putting together reactive networks using Reactive Extensions (e.g. RxJS in Javascript / Typescript), I often need logic that responds to a single event. `take(1)` is useful in this situation.

However, more than once, `take(1)` is a cursed operator, because it can easily cause an RxNetwork *to go dead*. This is because after a single event it completes.

It’d behoove one to remember this and make sure that’s really what you want. In this case, I was doing a `filter()` after a `take(1)` and it resulted in a reactive stream that send no events and just completed. I really needed to put the `filter` first.

TIL: git show <commit>:path/file.txt

Have you ever asked yourself, “How do I show a file at a particular commit or revision in its entirety?” “How do I print out a file not a diff in git?” “Show me a git file at a commit on stdout!” Here’s how you do it.

I knew about git show <commit> which shows a diff of all the files changed in a commit. You can even scope it with git show <commit> path/file.txt to show the diff for a particular file. Today I learned if you use a : (colon) instead of a (space) between the commit id and the file path git will instead show you the file in its entirety at that revision.

$ cd temp/
$ mkdir git_show_example
$ cd git_show_example/
$ git init
Initialized empty Git repository in .../temp/git_show_example/.git/
$ commit --allow-empty -m 'Initial commit'
[master (root-commit) 2f2f99d] Initial commit
$ echo 'Hello, World' > file.txt
$ git add file.txt
$ git commit -m 'Hello world'
[master 4bc4156] Hello world
 1 file changed, 1 insertion(+)
 create mode 100644 file.txt
$ echo 'Goodbye' > file.txt
$ git commit -a -m 'Goodbye'
[master 8af3b90] Goodbye
 1 file changed, 1 insertion(+), 1 deletion(-)
$ git show 4bc4156:file.txt
Hello, World

AWS ElasticBeanstalk

“any attached Amazon RDS DB instance will be deleted”. This boldfaced warning is presented when you sometimes need to resort to last measures to get an EB instance back on its feet. Lest you panic, you can easily see if your EB instance is managing any RDS instances by looking at the Database section of the configuration. It may well be you don’t have any databases at all — but they present this error message regardless of whether you do or do not have any.

Untitled Poem by Frances Rahn

I have lost my two babies – a boy and a girl.

And all that is left is a bootie and a curl.

Oh, the years seem like sixty instead of sixteen

Since I ruled their kingdom as nursery queen.

Dearest prince, and sweet princess, I long to retain

The vision of you in your childhood domain

Where a baby’s low coo, and a toddler’s soft kiss

Were loaned by the Master of heavenly bliss.

Though the princess stayed only from Spring until Fall

Yet there isn’t a soul who will ever know all

That she took of my heart when, without any fright,

She closed her blue eyes and slipped out in the night.

But the prince is a man now – that is, he’s almost

A man, and a fine one, I’m eager to boast.

I have done what I’m able since he was a lad

To help him distinguish the good from the bad.

Though I’m proud of these seventeen years in review,

Some times, like tonight, how I wish he were two.

How I yearn like a beggar on horseback to ride

On back through the years with them on my side,

Little dimple-kneed princess and apple-cheeked prince,

Much sweeter that anything I have known since.



JSTimers is not a registered callable module

This can happen if you have two versions of react-native installed. I use yarn to install dependencies, and normally fix this by adding a resolutions section to my package.json:

  "dependencies": {
    "react": "16.9.0",
    "react-native": "0.61.5",
  "resolutions": {
    "@types/react": "16.9.0",
    "react": "16.9.0",
    "react-native": "0.61.5"
  "devDependencies": {
    "@types/react": "^16.9.0",

Make certain that the versions are consistent — otherwise multiple versions may end up installed by react and some of those versions will not be able to connect to the native dependencies, resulting in an error like JSTimers is not a registered callable module or Module RCTDeviceEventEmitter is not a registered callable module.

Working Goldfish

Our goldfish have returned indoors after another successful summer of eating mosquito larvae in the water lily pond (a 25 gallon plastic tub). I overwinter the water lily bulb in a 5-gallon bucket that’s loosely covered in the basement.  Then in March I fill the outdoor pond and put the lily in the bottom.  I wait until I see a few larvae swimming in the pond before I put the goldfish out. That first day they gorge themselves on all the larvae.  We’ve had these two 5-cent comet goldfish for 10 years now. They absolutely thrive in the bucket all summer, and nary a mosquito larvae survives while they’re on duty. I don’t feed them at all — enough bugs and leaves and algae and who knows what comes along that they are fat as can be all summer. Every November I chip them out from beneath the frozen water and bring them inside.  Let them temperature acclimate in their own pond water in a bucket inside for 24 hours.  Then carefully net them into the aquarium that’s been running empty all summer. They live inside all winter — we do feed them now of course — no random bugs dropping in while inside (I HOPE).

Their names are Harold and Henry.

React-Native Viewpager

Android has a view called a “viewpager”. It’s sort of like iOS PageViewController. There are several efforts to bring this to react-native as a cross-platform solution. rn-viewpager is now abandoned, even though it worked great. react-native-app-intro-slider is interesting, but seems special purpose for doing welcome screens — it doesn’t allow other interesting use cases because it seems to assume it’s always the full width of the device window. react-native-viewpager is another one but it’s Android only.

One that seems often overlooked is good old tabview. This can be customized so that the tabs themselves look like paging dots and it already has a nice “viewpager” style animation.

So next time you’re googling for react-native viewpager, maybe consider tabview as an easy solution. It’s well supported by the community and doesn’t have as big a risk of being orphaned like rn-viewpager was.

“Cannot connect to iTunes Store”

If you’re trying to test a new in-app purchase on iOS, and you get this mysterious error:

Error Domain=SKErrorDomain Code=0 "Cannot connect to iTunes Store" UserInfo={NSLocalizedDescription=Cannot connect to iTunes Store}

… make sure you’re using a real device. This error will be given if you try to complete a purchase in the Simulator. That’s right, although you can list purchases in the simulator, actually buying something with a Test user in the sandbox environment will simply fail with this vague error.