difference between (defalias 'A (symbol-function 'B)) and (defalias 'A 'B)

Question

I was reading subr.el and saw this code:

(defalias \'backward-delete-char \'delete-backward-char)
(defalias \'search-forward-regexp (symbol-function \'re-search-         


        

Answer 1

The two defalias usages are slightly different. The first links the function cell for 'backward-delete-char to that of 'delete-backward-char. The second links the 'search-forward-regexp to the function that is currently called by 're-search-forward.

The difference is that if you later change the definition of 'delete-backward-char, 'backward-delete-char will now have the new behavior. Whereas in the second case, changing the function for 're-search-forward has no effect on the behavior of 'search-forward-regexp.

Perhaps some ascii art can help:

+-------------------------+     +-----------------+
|#| <-- |re-search-forward|
+-------------------------+     +-----------------+
                        ^       +---------------------+
                        \------ |search-forward-regexp|
                                +---------------------+

+----------------------------+     +--------------------+     +--------------------+
|#| <-- |delete-backward-char| <-- |backward-delete-char|
+----------------------------+     +--------------------+     +--------------------+

This documentation might help clear things up.