Three semi-obscure Elixir features

marick · April 1, 2021, 3:13am

I wrote about some Elixir features that are not that often useful, but I think are still good to know about: the process dictionary, handling calls to undefined functions, and Macro.decompose_call

This is in the context of explaining the guts of the Mockery package.

github.com

marick/mockery_extras/blob/main/how_mockery_works.md

# How Mockery works

Mockery uses two neat Erlang/Elixir features: the process dictionary
and custom handling of calls to module functions that don't exist
("method_missing"). Mockery Extras demonstrates a third: parsing
function calls in macros. I thought it would be fun to write them up.

## How to use Mockery

Starting with a fresh Elixir project, I'll write a function,
`days_from`, that calculates how many days lie between today and a
given date:

```elixir
iex(2)> days_from(~D[2000-01-01])
7759
```

The implementation is trivial:

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paulanthonywilson · April 1, 2021, 8:38am

Thanks for writing this up. It’s a really clear explanation of a couple of features. Even if I’ve no particular use for them right now it’s good to know they are there, in case of emergency.