Problems related to method calls in common. php in ThinkPHP

In ThinkPHP, I created a public function file common. php in the project Common, and wrote a toHtml () method in it. Then, you can directly call {$ list. article_content | toHtml =###} in the html template to call the methods in common. php in ThinkPHP.
I created a public function file Common. php in the project common, and wrote a toHtml () method in it.

Then, you can directly call {$ list. article_content | toHtml =###} in the html template ###}

This is correct. how can I execute this operation in a small project,
What about Call to undefined function toHtml () in another slightly complicated project?

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Use standard syntax to check whether the call is successful

TP groups. the common. php directory is different.
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Check whether the file is loaded and use the native php code to test whether the file is successful.
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Is it 2.0?

2.0 of available {: function ()}
If not, you can directly use the php source code.

If the methods in common. php are loaded successfully, they can be called directly in the template and program.
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It is best to use native. I like to use native in any framework.