Elixir Knowledge Patch (1.19–1.20, Phoenix 1.8, LiveView 1.0–1.1) Skill

Elixir Knowledge Patch (1.19–1.20, Phoenix 1.8, LiveView 1.0–1.1)

Baseline: Elixir 1.16, OTP 26, Phoenix 1.7, LiveView 0.x (pre-1.0), Ecto 3.11, GenServer, Supervisor, mix, ExUnit, dbg macro.

This patch covers Elixir 1.19–1.20-rc, Phoenix 1.8, and LiveView 1.0–1.1 (2024-12 to 2026-01).

Index

| Topic | File | Key Features | |-------|------|--------------| | Type System & Inference | references/elixir-type-system.md | Full expression inference, map key typing, struct update deprecation | | APIs, Mix & Compilation | references/elixir-apis-and-mix.md | New stdlib APIs, mix commands, lazy module loading, deprecations | | LiveView JS & Hooks | references/liveview-js-and-hooks.md | JS command targeting, colocated hooks, ViewHook class, programmable JS | | LiveView Templates & Streams | references/liveview-templates-and-streams.md | Keyed comprehensions, portals, ignore_attributes, LazyHTML migration | | Phoenix 1.8 | references/phoenix-1-8.md | Scopes, magic link auth, simplified layouts, security headers |

Quick Reference

Elixir 1.20 Type Inference

The compiler infers types from all expressions (not just patterns). Backward inference narrows argument types:

def sum_to_string(a, b), do: Integer.to_string(a + b)
# Infers a, b must be integer() (not float) because Integer.to_string requires integer

Cross-clause inference — later clauses know what previous clauses matched:

case System.get_env("VAR") do
  nil -> :not_found
  value -> String.upcase(value)  # value is binary(), not nil
end

Map Key Typing (1.20)

Map.put(map, :key, 123)      #=> %{..., key: integer()}
Map.delete(map, :key)         #=> %{..., key: not_set()}
Map.replace(map, :key, 123)   #=> %{..., key: if_set(integer())}

Struct Update Deprecation (1.19)

# Deprecated — requires prior pattern match:
def update(uri), do: %URI{uri | path: "/foo"}

# Correct:
def update(%URI{} = uri), do: %{uri | path: "/foo"}

New APIs at a Glance

| API | Version | Purpose | |-----|---------|---------| | Access.values/0 | 1.19 | Traverse all values in maps/keyword lists | | String.count/2 | 1.19 | Count pattern occurrences in string | | min/2, max/2 in guards | 1.19 | Guard-compatible min/max | | Integer.ceil_div/2 | 1.20 | Ceiling division | | Integer.popcount/1 | 1.20 | Count set bits | | IO.iodata_empty?/1 | 1.20 | Check if iodata is empty | | List.first!/1, List.last!/1 | 1.20 | Raise on empty list |

Breaking Changes (1.20)

# map.foo() with parens now RAISES (not warns) — use map.foo
# mod.foo without parens now RAISES — use mod.foo()

# File.stream! arg order swapped:
File.stream!(path, lines_or_bytes, modes)  # NEW order

# Bitstring size requires pin:
<<data::size(^size)>>  # was <<data::size(size)>>

LiveView Colocated Hooks (1.1)

<div id="sortable" phx-hook=".Sortable">...</div>
<script :type={Phoenix.LiveView.ColocatedHook} name=".Sortable">
  export default {
    mounted() { /* JS code here */ }
  }
</script>

Setup: add :phoenix_live_view to compilers: in mix.exs, import in app.js:

import {hooks as colocatedHooks} from "phoenix-colocated/my_app"
const liveSocket = new LiveSocket("/live", Socket, {hooks: {...colocatedHooks}})

LiveView Portals (1.1)

<.portal id="my-tooltip" target="body">
  <div class="tooltip">Content here</div>
</.portal>

Phoenix 1.8 Scopes

# Generated context functions take scope as first arg
def list_posts(%Scope{} = scope) do
  Repo.all(from p in Post, where: p.user_id == ^scope.user.id)
end

# LiveViews use socket.assigns.current_scope
def mount(_params, _session, socket) do
  Blog.subscribe_posts(socket.assigns.current_scope)
  {:ok, stream(socket, :posts, Blog.list_posts(socket.assigns.current_scope))}
end

Phoenix 1.8 Simplified Layouts

<Layouts.app flash={@flash}>
  <:breadcrumb><.link navigate={~p"/posts"}>Posts</.link></:breadcrumb>
  <p>My content</p>
</Layouts.app>

Single root.html.heex layout. Multiple app layouts: <Layouts.admin>, <Layouts.cart>, etc.

JS Command Targeting (LiveView 1.0)

<button phx-click={JS.add_class("highlight", to: {:closest, "tr"})}>Select</button>
<div phx-click={JS.show(to: {:inner, ".details"})}>Expand</div>

Keyed Comprehensions (LiveView 1.1)

<li :for={item <- @items} :key={item.id}>{item.name}</li>

Agent Skills: Elixir Knowledge Patch (1.19–1.20, Phoenix 1.8, LiveView 1.0–1.1)

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