toksdotdev

Someone asked a question some weeks back about why size_of::<Option<T>> is always double. Answer is because of alignment.

Explanation

How are Rust enum represented in C?

C doesn't have the ability to directly represent complex Rust enum, hence, the need for a workaround. To understand that, let's take a look at how Option<i32> is represnted in C.

E.g. Given:

rhmoller

use futures::task::{Context, Poll};
use std::cell::RefCell;
use std::future::Future;
use std::pin::Pin;
use std::rc::Rc;
use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;
use web_sys::HtmlImageElement;

/// A future for loading a [HtmlImageElement](https://docs.rs/web-sys/0.3.39/web_sys/struct.HtmlImageElement.html)

mbbx6spp

Cached and Persistent Nix shell with direnv integration

Problem being solved

• the default direnv Nix integration from projects loads a Nix shell every new terminal or every time shell.nix and/or default.nix changes. On larger projects with a lot of Nix shell dependencies, that can cause the terminal to take more than 6 seconds to load, which significantly degrades the developer experience (DX).
• when a developer garbage collects in their Nix store, often the Nix shell dependencies are deleted also which causes a slow start the next time the project’s Nix shell is requested, also degrading developer experience (DX).

Solution outline

• on first Nix shell load, the Nix shell is evaluated fully such that direnv dumps the environment from the spawn Nix shell process