Programmatically setting major mode of buffer with emacs lisp

I wish to programmatically set the major mode of a buffer. I have dug into the documentation, and the function set-buffer-major-mode only takes a buffer object. I am essentially looking for a function that takes a buffer object and a mode name.

Alternatively, I also tried using auto-mode-alist by forcing the buffer to have a file extension but that did not work even when I called the set-buffer-major-mode function.

Thanks for all the help!

Solution

The basics are that if you want to switch to my mode, all you have to do is to call my-mode, for example:

(with-current-buffer buffer
  (my-mode))

If you have a buffer and a variable bound to the major mode, you could use the following:

(with-current-buffer buffer
  (funcall the-mode-i-want))

Again, if you have a variable bound to a string, you have to convert it to a symbol using intern:

(with-current-buffer buffer
  (funcall (intern the-name-of-the-mode-i-want)))