Migration

You can incrementally port code to use XHP.

Assume your output is currently handled by the following function, which might be called from many places.

function render_component(string $text, Uri $uri): string {
  $uri = htmlspecialchars($uri->toString());
  $text = htmlspecialchars($text);
  return "<a href=\"$uri\">$text</a>";
}

Convert Leaf Functions

You can start by simply using XHP in render_component:

async function render_component(string $text, Uri $uri): Awaitable<string> {
  $link = <a href={$uri->toString()}>{$text}</a>;
  return await $link->toStringAsync();
  // or HH\Asio\join if converting all callers to async is hard
}

You are converting render_component into a safer function without the need for explicit escaping, etc. But you are still passing strings around in the end.

Use a Class

You could make render_component into a class:

namespace ui;

class link extends x\element {
  attribute Uri uri @required;
  attribute string text @required;
  protected async function renderAsync(): Awaitable<x\node> {
    return
      <a href={$this->:uri->toString()}>{$this->:text}</a>;
  }
}

Keep a legacy render_component around while you are converting the old code that uses render_component to use the class.

async function render_component(string $text, Uri $uri): Awaitable<string> {
  return await (<ui:link uri={$uri} text={$text} />)->toStringAsync();
}