add-to-list or push? Is there any disadvantage in using one over the other?

Question

I've added a line in my early-init.el file that sets a background color to prevent the glare during startup.

;; Customize background color to prevent startup glare
(add-to-list 'default-frame-alist
             '(background-color . "#fff2f3"))

However, I've noticed that the code can also be written as:

;; Customize background color to prevent startup glare
(push '(background-color . "#fff2f3") default-frame-alist)

They both achieve the same result. I was wondering if there is any disadvantage in using one method over the other?

Answer 1

The doc makes clear what the differences are.

If you obtain the variable (its symbol) programmatically, i.e., you evaluate something to get the symbol, then use add-to-list. (Otherwise, with push you need to invoke eval to get the value of the resulting symbol.)

push adds a list element unconditionally; add-to-list adds an element only if not already in the list. However, you can use macro cl-pushnew to add an element only if not already present.

In Elisp, push doesn't let you provide the equivalent of add-to-list's args APPEND and COMPARE-FN. However, you can use macro cl-pushnew to get the effect of both.

The differences generally don't matter for the use case you describe: simply adding an element to a configuration variable in your init file. (If it matters to you whether the element is added if it's already present, then use add-to-list or cl-pushnew.)

Generally speaking add-to-list is more similar to cl-pushnew than it is to push.