ollran

ollran

Pattern matching against arbitrary sized tuple

How can I pattern match against an arbitrary sized tuple? This works:

{status, _, _} = {:ok, 1, 2}

But what if I don’t know the structure of the tuple on the right side and I only care about the first element? This doesn’t work:

{status, _} = {:ok, 1, 2, 3, 4, 5, 6}
{status, _} = {:ok, {:random, :things}, [1, 2, 3]}

Is it possible to get the first value from the tuple with pattern matching?

First 6 of 6 Posts Switch mode

NobbZ

NobbZ

No. A tuple is of fixed size.

You can either use status = elem({:ok, 1, 2, 3}, 0) or [status | _] = Tuple.to_list({:ok, 1, 2, 3}.

lpil

lpil

Creator of Gleam

Tuple.to_list/1 will allocate a new list, Kernel.elem/2 can be used to retrieve the first element without creating this intermediate list :slight_smile:

dkuku

dkuku

would be handy to have some macro that generates the missing underscores:

 {:ok, info} <- :file.read_file_info(pid),
 {:file_info, file_size, _, _, _, _, _, _, _, _, _, _, _, _} <- info,
{:file_info, file_size, _escape_next(12)} <- info,
ityonemo

ityonemo

for that particular tuple, I think you can use the Record module.

dkuku

dkuku

Thanks, this makes the code much more readable, not much examples for this module, if someone needs one for this particular case:

defmodule FileInfo do
  require Record
  Record.defrecord :file_info, Record.extract(:file_info, from_lib: "kernel/include/file.hrl")
end

and then instead my previous line I have a keyword list that can be accessed with

iex(3)> import FileInfo
FileInfo
iex(4)> info
{:file_info, 2333891, :regular, :read, {{2020, 12, 29}, {19, 18, 12}},
 {{2020, 12, 29}, {19, 27, 58}}, {{2020, 12, 29}, {19, 27, 58}}, 33188, 1,
 66310, 0, 302070, 33, 19}
iex(5)> file_info(info)
[
  size: 2333891,
  type: :regular,
  access: :read,
  atime: {{2020, 12, 29}, {19, 18, 12}},
  mtime: {{2020, 12, 29}, {19, 27, 58}},
  ctime: {{2020, 12, 29}, {19, 27, 58}},
  mode: 33188,
  links: 1,
  major_device: 66310,
  minor_device: 0,
  inode: 302070,
  uid: 33,
  gid: 19
]
iex(6)> file_info(info, :size)
2333891

glmeocci

glmeocci

I’d love it!

{:file_info, file_sieze | _the_rest_as_tuple}  <- info
— All posts loaded —

Where Next?

Trending in Questions Top

stjefim
Hello! Suppose you are building workflow (order / task / payment) processing system with the following requirements: Each workflow con...
New
jonnycharles
I’m in search of an Elixir library that offers PDF generation capabilities similar to Ruby’s Prawn. While there have been discussions abo...
New
spammy
I’m looking to build a personal workflow to quickly deploy web applications written in elixir/phoenix, for local consumption (ie not on t...
New
silverdr
Using Phoenix.LiveView.TagEngine as an EEx.Engine is deprecated! To compile HEEx, use Phoenix.LiveView.TagEngine.compile/2 instead. Sta...
New
dli
Before I dive in myself, did anyone successfully sprinkle Hologram into their existing LiveView app? Looking for hints regarding: Addi...
New
bottlenecked
Hi all, I wanted to ask how the community is dealing with post-release steps. Today we have Ecto migrations, which make sure that the db...
New
michallepicki
I am using Oban and occasionally, shortly after a deployment, a handful of jobs can fail because of dependency on other parts of the syst...
New

Other Trending Topics Top

JesseHerrick
Hey, I’m Jesse and I’m the main contributor behind Dexter, a full-featured, lightning-fast Elixir LSP optimized for large codebases. It s...
New
jimsynz
Beam Bots (or just BB for short) is a framework for building fault-tolerant robotics applications in Elixir using familiar OTP patterns. ...
New
Damirados
Hello everyone. After busy few months I am happy to announce v0.1.0 of Emerge &amp; Solve. They are GUI (Emerge) and State management (S...
New
ausimian
Emily is an Elixir library that runs Nx computations on Apple’s MLX. Install it as the default Nx backend and Nx, defn, Axon, Nx.Serving,...
New
type1fool
I just stumbled on a newly redesigned elixir-lang.org. :tada: It looks like @Software_Mansion did the work, and I think it is generally a...
New
juhalehtonen
There has been a thread to discuss the Stack Overflow Developer Survey on this forum every year since 2018, so here’s yet another one for...
New

We're in Beta

About us Mission Statement