Singleton: Difference between revisions
→{{header|TXR}}: New section.
Thundergnat (talk | contribs) m (syntax highlighting fixup automation) |
(→{{header|TXR}}: New section.) |
||
Line 2,156:
I am a singleton
</pre>
=={{header|TXR}}==
<syntaxhighlight lang="txrlisp">;; Custom (:singleton) clause which adds behavior to a class
;; asserting against multiple instantiation.
(define-struct-clause :singleton ()
^((:static inst-count 0)
(:postinit (me)
(assert (<= (inc me.inst-count) 1)))))
(defstruct singleton-one ()
(:singleton)
(:method speak (me)
(put-line "I am singleton-one")))
(defstruct singleton-two ()
(:singleton)
(:method speak (me)
(put-line "I am singleton-two")))
;; Test
;; Global singleton
(defvarl s1 (new singleton-one))
;; Local singleton in function (like static in C)
;; load-time evaluates once.
(defun fn ()
(let ((s2 (load-time (new singleton-two))))
s2.(speak)))
s1.(speak)
(fn) ;; multiple calls to fn don't re-instantiate singelton-two
(fn)
(put-line "so far, so good")
(new singleton-two) ;; assertion gooes off</syntaxhighlight>
{{out}}
<pre>I am singleton-one
I am singleton-two
I am singleton-two
so far, so good
txr: unhandled exception of type assert:
txr: assertion (<= (inc me.inst-count)
1) failed in singleton.tl:6
txr: during evaluation at singleton.tl:6 of form (sys:rt-assert-fail "singleton.tl"
6 '(<= (inc me.inst-count)
1))</pre>
=={{header|Vala}}==
| |||