How to print directly to HAML buffer?

I'm trying this (haml 6.3.0):

def my_helper
  Haml::Helpers.html_concat('Hello, world!')
end

Then, in my.haml I do this:

- my_helper

However, I'm getting:

NoMethodError: undefined method `html_concat' for Haml::Helpers:Module

What is the right method? Please, don't suggest to use = my_helper. My real case is much more complicated and I do need to print to the buffer directly instead of returning a string.

The function haml_concat was removed in 6.0.0 according to the changelog. The function used to use methods that modified the internal buffer and the changelog says this part of the API has been removed after 6.0.0 and there is no alternative:

Ones that rely on Haml::Buffer have no direct alternative by design. They existed at the cost of performance. You need to define a helper, instantiate a String buffer in it, append stuff to it, and call it inside =.

So it looks like there is no way to write to the Haml buffer without = anymore.