Go-like defer 'keyword' for shell

defer.sh

#!/bin/sh
DEFER=
defer() {
    DEFER="$*; ${DEFER}"
    trap "{ $DEFER }" EXIT
}

The correct noun form of the adjective "idempotent" is "idempotence", not *idempotency*.
An idempotent operation is one that has the same effect whether you apply it once or multiple times.
Not leaking (which your trap wrapper could help with) is one aspect aspect of this but not the main meaning.

This will not handle spaces correctly, try for example

defer echo "a  b" # two spaces between 'a' and 'b'

the output will have one space:

a b

Looking at the ongoing comments on HN and here, I'll go with @charles-dyfis-net's version which handle spaces correctly (bash5.0+ only).

#!/usr/bin/env bash

DEFER=

defer() {
    DEFER="${*@Q}; ${DEFER}"
    trap "{ $DEFER }" EXIT
}

# some tests
TEMP=$(mktemp)
touch "/tmp/a  b"
defer rm -vf "$TEMP" "/tmp/a  b"
ls -lsah "$TEMP"
ls -lsah "/tmp/a  b"

The solutions for shell seemed too complicated or wrong.

As an addendum (since the suggestions I made above are applicable either to bash 5+ or shells with the ksh93 printf %q extension such as bash or zsh):

For folks who want both safety and compatibility with /bin/sh, I'd suggest encapsulating cleanup code in functions (with no arguments -- getting content from variables only) and then passing the names of those functions to defer. rm_tmp_ab() { rm -vf "$TEMP" "/tmp/a b"; }; defer rm_tmp_ab f/e.