I tried to use the wonderful dump function from the var-dumper bundle in symfony 4 and for some reason I get the following error:
Failed to start the session because headers have already been sent by "vendor\symfony\var-dumper\Dumper\AbstractDumper.php" at line 181.
Additionally, when I try to use the {% dump foo %} tag in a twig template I get an error:
Unknown "dump" tag.
Can anyone help me?
A guy named Simon Waldburger mentioned in the lesson's comments that installing "debug" fixed the issue (it fixed it for me). The instruction was in the next lesson.
composer require debug --dev
iiirxs is also correct, to output dump in twig file, do
{{ dump(variable) }}
来源：https://stackoverflow.com/questions/48304155/symfony-4-var-dumper-not-working-properly