commands

How to create a Scala 3 (Dotty) project with SBT

I can never remember how to create a Scala 3 (Dotty) project with SBT (in early 2019), so:

# create a new Dotty project
sbt new lampepfl/dotty.g8

# create a dotty project that cross compiles with scala 2
sbt new lampepfl/dotty-cross.g8

# start a dotty reply from within your sbt project
$ sbt

> console
scala> _

Here’s what an example interaction looks like — include SBT renaming my directory name to all lowercase, which brings me no joy:

Notes on how to build and run an Android application from the command line alvin March 6, 2019 - 8:21pm

As a brief note to self, this is how I compiled/built an Android application (APK) from the MacOS command line and then ran it in an emulator. I include both my application- and system-specific notes, as well as the more generic commands I found at this Android.com URL:

A Drush 9 list of commands (for Drupal 8)

I’m sure there’s something I’m missing here, but ... as I’m just getting started using Drush 9 to manage a Drupal 8 website, I can’t find a list of Drush 9 commands on the drush.org website. Therefore, in an effort to make my life easier (and hopefully yours), here’s a list of Drush 9 commands.

You can run the `javap` command inside the Scala REPL

As shown in the image, I was just reminded that you can run javap inside the Scala REPL. The REPL help command shows some other things you can do:

scala> :help

All commands can be abbreviated, e.g., :he instead of :help.
:edit <id>|<line>        edit history
:help [command]          print this summary or command-specific help
:history [num]           show the history (optional num is commands to show)
:h? <string>             search the history
:imports [name name ...] show import history, identifying sources of names
:implicits [-v]          show the implicits in scope
:javap <path|class>      disassemble a file or class name
:line <id>|<line>        place line(s) at the end of history
:load <path>             interpret lines in a file
:paste [-raw] [path]     enter paste mode or paste a file
:power                   enable power user mode
:quit                    exit the interpreter
:replay [options]        reset the repl and replay all previous commands
:require <path>          add a jar to the classpath
:reset [options]         reset the repl to its initial state, forgetting all session entries
:save <path>             save replayable session to a file
:sh <command line>       run a shell command (result is implicitly => List[String])
:settings <options>      update compiler options, if possible; see reset
:silent                  disable/enable automatic printing of results
:type [-v] <expr>        display the type of an expression without evaluating it
:kind [-v] <type>        display the kind of a type. see also :help kind
:warnings                show the suppressed warnings from the most recent line which had any

More Scala/javap examples

Here are a couple more javap examples in the Scala REPL that help to show what details are available:

scala> class Person (var name: String, var age: Int)
defined class Person

scala> :javap -public Person
Compiled from "<console>"
public class $line3.$read$$iw$$iw$Person {
  public java.lang.String name();
  public void name_$eq(java.lang.String);
  public int age();
  public void age_$eq(int);
  public $line3.$read$$iw$$iw$Person(java.lang.String, int);
}

scala> :javap -private Person
Compiled from "<console>"
public class $line3.$read$$iw$$iw$Person {
  private java.lang.String name;
  private int age;
  public java.lang.String name();
  public void name_$eq(java.lang.String);
  public int age();
  public void age_$eq(int);
  public $line3.$read$$iw$$iw$Person(java.lang.String, int);
}

javap help

Finally, here’s the output from the javap -help command that helps to explain that output:

> javap -help
Usage: javap <options> <classes>
where possible options include:
  -help  --help  -?        Print this usage message
  -version                 Version information
  -v  -verbose             Print additional information
  -l                       Print line number and local variable tables
  -public                  Show only public classes and members
  -protected               Show protected/public classes and members
  -package                 Show package/protected/public classes
                           and members (default)
  -p  -private             Show all classes and members
  -c                       Disassemble the code
  -s                       Print internal type signatures
  -sysinfo                 Show system info (path, size, date, MD5 hash)
                           of class being processed
  -constants               Show final constants
  -classpath <path>        Specify where to find user class files
  -cp <path>               Specify where to find user class files
  -bootclasspath <path>    Override location of bootstrap class files

If you ever want to use javap inside the Scala REPL, I hope this information is helpful.

Free Unix/Linux and vi/vim cheat sheets

Way back in the 1990s I created some “cheat sheets” for Unix training classes that I taught. Somewhere in the 2000s I updated them to make sure they worked with Linux as well, Here then are two Unix/Linux cheat sheets I created (way back when) that you can print out if you’re just learning Linux and the vi/vim editor: