различие между (defalias '(Функция символа 'B)) и (defalias ''B)
Это очень просто. предположим, клетка - это объект, положение которого нужно выяснить.
UITableView* table = (UITableView *)[cell superview];
NSIndexPath* pathOfTheCell = [table indexPathForCell:cell];
NSInteger sectionOfTheCell = [pathOfTheCell section];
NSInteger rowOfTheCell = [pathOfTheCell row];
2 ответа
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:
+-------------------------+ +-----------------+
|#<subr re-search-forward>| <-- |re-search-forward|
+-------------------------+ +-----------------+
^ +---------------------+
\------ |search-forward-regexp|
+---------------------+
+----------------------------+ +--------------------+ +--------------------+
|#<subr delete-backward-char>| <-- |delete-backward-char| <-- |backward-delete-char|
+----------------------------+ +--------------------+ +--------------------+
This documentation might help clear things up.
Ну, это действительно не то же самое ... Вот небольшая игра, в которую я только что играл:
(defun a () (message "hello"))
a
(a)
"hello"
(defalias 'b (symbol-function 'a))
(lambda nil (message "hello"))
(defalias 'c 'a)
a
(b)
"hello"
(c)
"hello"
(defun a () (message "howdy"))
a
(a)
"howdy"
(b)
"hello"
(c)
"howdy" ' c changed meaning, b did not...