Now ask it what happened

Here is the difference. A plain pipeline hands you the final value and nothing else: if the title came out wrong, you are left guessing which step broke it. The hub kept notes. Ask it what happened:

<?php

use Keaton\PipeDream\PipeHub;

$post = (object) ['title' => '  hello,   PIPE dream  '];

$envelope = PipeHub::create()
    ->addPipes([
        fn ($post) => $post->title = trim($post->title),
        fn ($post) => $post->title = preg_replace('/\s+/', ' ', $post->title),
        fn ($post) => $post->title = ucwords(strtolower($post->title)),
    ])
    ->sendIt($post);

foreach ($envelope->logs() as $record) {
    printf("%-11s %-24s %s\n", $record['type'], $record['key'], $record['data']);
}

info        PipeHub:sendIt           Sending subject through all pipes
timerStart  Closure@hub-log.php:9    Executing rule Closure@hub-log.php:9
returnValue Closure@hub-log.php:9    hello,   PIPE dream
timerEnd    Closure@hub-log.php:9    Finished executing rule Closure@hub-log.php:9
timerStart  Closure@hub-log.php:10   Executing rule Closure@hub-log.php:10
returnValue Closure@hub-log.php:10   hello, PIPE dream
timerEnd    Closure@hub-log.php:10   Finished executing rule Closure@hub-log.php:10
timerStart  Closure@hub-log.php:11   Executing rule Closure@hub-log.php:11
returnValue Closure@hub-log.php:11   Hello, Pipe Dream
timerEnd    Closure@hub-log.php:11   Finished executing rule Closure@hub-log.php:11
info        PipeHub:sendIt           Finalized result!

Every pipe was timed, and what each one returned was recorded. You can see exactly where hello, PIPE dream became Hello, Pipe Dream, without adding a single line of logging to your code. $envelope->results() holds the same results, ready to check in code.

Now break it on purpose. Change the second step so it eats every space, and run the hub again:

<?php

use Keaton\PipeDream\PipeHub;

$post = (object) ['title' => '  hello,   PIPE dream  '];

$envelope = PipeHub::create()
    ->addPipes([
        fn ($post) => $post->title = trim($post->title),
        fn ($post) => $post->title = preg_replace('/\s+/', '', $post->title), // oops: '' instead of ' '
        fn ($post) => $post->title = ucwords(strtolower($post->title)),
    ])
    ->sendIt($post);

foreach ($envelope->logs() as $record) {
    if ($record['type'] === 'returnValue') {
        printf("%-30s %s\n", $record['key'], $record['data']);
    }
}

Closure@hub-log-broken.php:9   hello,   PIPE dream
Closure@hub-log-broken.php:10  hello,PIPEdream
Closure@hub-log-broken.php:11  Hello,pipedream

You don't have to guess which step ate the spaces. The log already points at the second one: it's the first line where they're gone.

That's the whole difference. A pipeline tells you the answer. A hub hands you the receipt.

And that's only the start. Once every step is a named, recorded thing, a lot more opens up:

• Rules as classes: each pipe becomes a small, testable class with a name, so the log reads like a description of your business.
• Stacked hubs: group steps into stages and run the stages as one flow, with one log.
• Control flow: skip a step, stop a flow early, redirect, or catch a failure without losing the log.
• Saved runs: store every log and query it later: which runs hit problems, and exactly where.
• A flow you can draw: read a flow back and render it as a page, then watch real traffic move through it.

All of it builds on what you just saw. The docs pick it up from here.