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New in Symfony 4.3: Iterable progress bars

Contributed by
Jérôme Vasseur
in #29753.

The common workflow for Symfony Console progress bars is to start them, advance them according to your task progress and finish them:

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use Symfony\Component\Console\Helper\ProgressBar;

$progressBar = new ProgressBar($output);
$progressBar->start();

// ... do some work
$progressBar->advance();

// needed to ensure that the bar reaches 100%
$progressBar->finish();

In Symfony 4.3 we've improved this workflow when you work with iterable variables (such as arrays or generators). Thanks to the new iterate() method, you can pass the iterable variable and the progress bar starts, advances and finishes automatically.

Consider the following simple PHP generator:

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$iterable = function () {
    yield 1;
    yield 2;
    // ...
};

You can turn this into a progress bar as follows:

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use Symfony\Component\Console\Helper\ProgressBar;

$progressBar = new ProgressBar($output);

foreach ($progressBar->iterate($iterable) as $value) {
    // ... do some work
}

The output in your terminal will be the following:

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0 [>---------------------------]
1 [==============>-------------]
2 [============================]

If the iterable variable is countable, the max steps of the progress bar is set automatically. Otherwise, you can pass the number of steps as the second optional argument of iterate():

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foreach ($progressBar->iterate($iterable, 100) as $value) {
    // ... do some work
}

Comments

A Generator that you pass to iterate() is not countable. So the ProgressBar does not know automatically that there will be maximum of two items. The given output does not fit with an indeterminate progress bar. Alternatively you can use `$progressBar->iterate($iterable, 2)`
Very nice, this makes the flow much clear!
@Tobias thanks for your comment. I've updated the post to fix the progress bar output error and to mention the countable behavior.

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