I have a function defined in my init.el:
(defun bind-key (keymap)
(evil-define-key '(normal insert) keymap (kbd "C-=") 'some-function))
(bind-key 'c++-mode-map)
But evil-define-key does not bind the C-= to some-function in keymap.
However, invoke evil-define-key directly is ok:
(evil-define-key '(normal insert) c++-mode-map (kbd "C-=") 'some-function)
I have tried:
(bind-key 'c++-mode-map)
(bind-key c++-mode-map)
Neither works.
I have googled for passing keymaps to a function, but found no solution. Then, I noticed evil-define-key is a macro. But I can not found solutions in this situation.
How can I get bind-key to work? By passing a keymap to it, the function binds C-= to some-function in in the keymap?
As you've noticed, this is trickier than it looks because evil-define-key is a macro (defined here). It takes a symbol that names a keymap variable, and binds the key once that variable has been defined. However, in this case it gets the symbol keymap instead of c++-mode-map, since a macro invocation receives as arguments the literal values in the call.
You can get around this by changing your own function into a macro. That means that instead of just running some code, it needs to return some code that then gets evaluated. Like this:
(defmacro bind-key (keymap)
`(evil-define-key '(normal insert) ,keymap (kbd "C-=") 'some-function))
The backquote introduces a form that gets returned verbatim, except for values inside it preceded by a comma.
Invoke it with (bind-key c++-mode-map), and it should be equivalent to your explicit call to evil-define-key.