Re: [PATCH] extend map-into

[Stefan Monnier]

> attached.

Thanks, installed into `master` with minor tweaks (e.g. the NEWS entry
was misplaced, and I changed the defsubst into a defun because the
function itself contains a loop so the overhead of the function call is
unlikely to be significant in proportion).


        Stefan


> From 7a1b42b1b58f7b0ee20ef24e9e73bce045a1987b Mon Sep 17 00:00:00 2001
> From: Andrea Corallo <address@hidden>
> Date: Sun, 6 Oct 2019 22:43:11 +0200
> Subject: [PATCH] Extend 'map-into' for better control on hash table creation.
>
> ---
>  etc/NEWS                          |  4 ++++
>  lisp/emacs-lisp/map.el            | 29 +++++++++++++++++++++--------
>  test/lisp/emacs-lisp/map-tests.el |  5 ++++-
>  3 files changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/etc/NEWS b/etc/NEWS
> index c8cc753..5942a32 100644
> --- a/etc/NEWS
> +++ b/etc/NEWS
> @@ -24,6 +24,10 @@ applies, and please also update docstrings as needed.
>  
>  * Installation Changes in Emacs 27.1
>  
> +** Extend function 'map-into'.
> +Add a 'map-into' method to have hash table creation parameters
> +tweak-able.
> +
>  ** Emacs now uses GMP, the GNU Multiple Precision library.
>  By default, if 'configure' does not find a suitable libgmp, it
>  arranges for the included mini-gmp library to be built and used.
> diff --git a/lisp/emacs-lisp/map.el b/lisp/emacs-lisp/map.el
> index 54e802e..dfc1500 100644
> --- a/lisp/emacs-lisp/map.el
> +++ b/lisp/emacs-lisp/map.el
> @@ -338,7 +338,8 @@ map-every-p
>      t))
>  
>  (defun map-merge (type &rest maps)
> -  "Merge into a map of type TYPE all the key/value pairs in MAPS."
> +  "Merge into a map of type TYPE all the key/value pairs in MAPS.
> +See `map-into' for all supported values of TYPE."
>    (let ((result (map-into (pop maps) type)))
>      (while maps
>        ;; FIXME: When `type' is `list', we get an O(N^2) behavior.
> @@ -354,7 +355,8 @@ map-merge-with
>    "Merge into a map of type TYPE all the key/value pairs in MAPS.
>  When two maps contain the same key (`eql'), call FUNCTION on the two
>  values and use the value returned by it.
> -MAP can be a list, hash-table or array."
> +MAP can be a list, hash-table or array.
> +See `map-into' for all supported values of TYPE."
>    (let ((result (map-into (pop maps) type))
>          (not-found (cons nil nil)))
>      (while maps
> @@ -458,17 +460,28 @@ map-do
>                       (funcall function index elt))
>                     array))
>  
> -(cl-defmethod map-into (map (_type (eql hash-table)))
> -  "Convert MAP into a hash-table."
> -  ;; FIXME: Just knowing we want a hash-table is insufficient, since that
> -  ;; doesn't tell us the test function to use with it!
> -  (let ((ht (make-hash-table :size (map-length map)
> -                             :test 'equal)))
> +(defsubst map--into-hash (map keyword-args)
> +  "Convert MAP into a hash-table.
> +KEYWORD-ARGS are forwarded to `make-hash-table'."
> +  (let ((ht (apply #'make-hash-table keyword-args)))
>      (map-apply (lambda (key value)
>                   (setf (map-elt ht key) value))
>                 map)
>      ht))
>  
> +(cl-defmethod map-into (map (_type (eql hash-table)))
> +  "Convert MAP into a hash-table."
> +  (map--into-hash map (list :size (map-length map) :test 'equal)))
> +
> +(cl-defmethod map-into (map (args (head hash-table)))
> +  "Convert MAP into a hash-table.
> +ARGS is a list where the car is 'hash-table' and the cdr are the keyword-args
> + forwarded to `make-hash-table'.
> +
> +Example:
> +    (map-into '((1 . 3)) '(hash-table :test eql))"
> +  (map--into-hash map (cdr args)))
> +
>  (defun map--make-pcase-bindings (args)
>    "Return a list of pcase bindings from ARGS to the elements of a map."
>    (seq-map (lambda (elt)
> diff --git a/test/lisp/emacs-lisp/map-tests.el 
> b/test/lisp/emacs-lisp/map-tests.el
> index a54af80..9f61511 100644
> --- a/test/lisp/emacs-lisp/map-tests.el
> +++ b/test/lisp/emacs-lisp/map-tests.el
> @@ -340,7 +340,8 @@ test-map-every-p
>  
>  (ert-deftest test-map-into ()
>    (let* ((alist '((a . 1) (b . 2)))
> -         (ht (map-into alist 'hash-table)))
> +         (ht (map-into alist 'hash-table))
> +         (ht2 (map-into alist '(hash-table :test eq))))
>      (should (hash-table-p ht))
>      (should (equal (map-into (map-into alist 'hash-table) 'list)
>                     alist))
> @@ -349,6 +350,8 @@ test-map-into
>                     (map-keys ht)))
>      (should (equal (map-values (map-into (map-into ht 'list) 'hash-table))
>                     (map-values ht)))
> +    (should (equal (map-into ht 'alist) (map-into ht2 'alist)))
> +    (should (eq (hash-table-test ht2) 'eq))
>      (should (null (map-into nil 'list)))
>      (should (map-empty-p (map-into nil 'hash-table)))
>      (should-error (map-into [1 2 3] 'string))))