shaolang
Real-World Event Sourcing: `handle_command` for subtract doesn't make sense (pg 8)
The book implements handle_command/2 for :sub as follows:
def handle_command(%{value: val}, %{cmd: :sub, value: v}) do
%{event_type: :value_subtracted, max(@min_state_value, val - v)
end
The value in the created event is the result expected after subtraction, i.e., it is not the subtrahend. It can be reimplemented as follows instead:
def handle_command(%{value: val}, %{cmd: :sub, value: v) do
subtrahend = if(val >= v, do: v, else: val)
%{event_type: :value_subtracted, value: subtrahend}
end
First Post!
dmitrykleymenov
I’ve found the same issue, but think the code should be like:
def handle_command(%{value: val}, %{cmd: :sub, value: v}) do
%{event_type: :value_subtracted, value: min(val - @min_state_value, v)}
end
In this case we can use @min_state_value correctly(not only 0)
Popular Pragmatic Bookshelf topics
page 20: … protoc command…
I had to additionally run the following go get commands in order to be able to compile protobuf code using go...
New
Some minor things in the paper edition that says “3 2020” on the title page verso, not mentioned in the book’s errata online:
p. 186 But...
New
The following is cross-posted from the original Ray Tracer Challenge forum, from a post by garfieldnate. I’m cross-posting it so that the...
New
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
New
A Common-Sense Guide to Data Structures and Algorithms, Second Edition by Jay Wengrow @jaywengrow
Hi,
I have the paperback version of t...
New
Dear Sophie.
I tried to do the “Authorization” exercise and have two questions:
When trying to plug in an email-service, I found the ...
New
I’m under the impression that when the reader gets to page 136 (“View Data with the Database Inspector”), the code SHOULD be able to buil...
New
The test is as follows:
Scenario: Intersecting a scaled sphere with a ray
Given r ← ray(point(0, 0, -5), vector(0, 0, 1))
And s ← sphere...
New
@mfazio23
I’m following the indications of the book and arriver ad chapter 10, but the app cannot be compiled due to an error in the Bas...
New
I just bought this book to learn about Android development, and I’m already running into a major issue in Ch. 1, p. 20: “Update activity...
New
Other popular topics
@AstonJ prompted me to open this topic after I mentioned in the lockdown thread how I started to do a lot more for my fitness.
https://f...
New
Curious to know which languages and frameworks you’re all thinking about learning next :upside_down_face:
Perhaps if there’s enough peop...
New
I’ve been hearing quite a lot of comments relating to the sound of a keyboard, with one of the most desirable of these called ‘thock’, he...
New
Rust is an exciting new programming language combining the power of C with memory safety, fearless concurrency, and productivity boosters...
New
Small essay with thoughts on macOS vs. Linux:
I know @Exadra37 is just waiting around the corner to scream at me “I TOLD YOU SO!!!” but I...
New
Hello everyone! This thread is to tell you about what authors from The Pragmatic Bookshelf are writing on Medium.
New
Saw this on TikTok of all places! :lol:
Anyone heard of them before?
Lite:
New
Hi folks,
I don’t know if I saw this here but, here’s a new programming language, called Roc
Reminds me a bit of Elm and thus Haskell. ...
New
Rails 7 completely redefines what it means to produce fantastic user experiences and provides a way to achieve all the benefits of single...
New
A concise guide to MySQL 9 database administration, covering fundamental concepts, techniques, and best practices.
Neil Smyth
MySQL...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /ruby
- /wasm
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /haskell
- /java
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /html
- /opensuse
- /centos
- /zig
- /deepseek
- /php
- /scala
- /sublime-text
- /lisp
- /textmate
- /react-native
- /debian
- /nixos
- /agda
- /kubuntu
- /arch-linux
- /django
- /deno
- /revery
- /nodejs
- /ubuntu
- /spring
- /manjaro
- /diversity
- /lua
- /julia
- /markdown
- /c
Devtalk Sponsors
Practical resources that improve the lives of professional developers.
We build trusted fault-tolerant systems that scale to billions of users.
Real-time error tracking, performance insights, and observability for devs.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Develop your skills with books, videos, and courses.
Catch errors, track performance, monitor hosts and more.
Enabling companies to succeed by building software people love.
Courses that move you from confusion to "Aha, now I get it!"