create bin% class and add factory methods

gstreamer/bin.rkt

@@ -0,0 +1,46 @@
+#lang racket/base
+
+(require (except-in ffi/unsafe/introspection
+                    send get-field set-field! field-bound? is-a? is-a?/c)
+         racket/class
+         racket/contract
+         "gst.rkt"
+         "element.rkt")
+
+(provide (contract-out [bin%
+                        (class/c
+                         [add
+                          (->m (is-a?/c element%) boolean?)]
+                         [remove
+                          (->m (is-a?/c element%) boolean?)]
+                         [get-by-name
+                          (->m string? (or/c (is-a?/c element%) false/c))]
+                         [add-many
+                          (->m (is-a?/c element%) (is-a?/c element%) ... boolean?)]
+                         [find-unlinked-pad
+                          (->m (gi-enum-value/c pad-direction) (or/c (is-a?/c pad%) false/c))]
+                         [sync-children-states
+                          (->m boolean?)])]))
+
+(define bin-mixin
+  (make-gobject-delegate add
+                         remove
+                         get-by-name
+                         find-unlinked-pad
+                         sync-children-states))
+
+(define bin%
+  (class (bin-mixin element%)
+    (super-new)
+    (inherit-field pointer)
+    (define/override (get-by-name name)
+      (let ([el (super get-by-name name)])
+        (and el
+             (new element% [pointer el]))))
+    (define/public (add-many el_1 . els)
+      (for/and ([el (list* el_1 els)])
+        (send this add el)))
+    (define/override (find-unlinked-pad direction)
+      (let ([pad (super find-unlinked-pad direction)])
+        (and pad
+             (new pad% [pointer pad]))))))

gstreamer/main.rkt

@@ -7,17 +7,16 @@
          racket/class
          racket/contract
          "gst.rkt"
-         "element.rkt")
+         "element.rkt"
+         "bin.rkt")
 
 (provide (all-from-out "gst.rkt"
-                       "element.rkt")
-         bin-add-many
+                       "element.rkt"
+                       "bin.rkt")
          seconds
-         element-link-many
          _input-selector-sync-mode
          _video-test-src-pattern
          _audio-test-src-wave
-         gst-compose
          (contract-out [element-factory%-find
                         (-> string? (or/c false/c
                                           (is-a?/c element-factory%)))]
@@ -33,7 +32,15 @@
                        [ghost-pad%-new-no-target
                         (-> (or/c string? false/c) (gi-enum-value/c pad-direction)
                             (or/c (is-a?/c ghost-pad%)
-                                  false/c))]))
+                                  false/c))]
+                       [bin%-new
+                        (->* ()
+                             ((or/c string? false/c))
+                             (is-a?/c bin%))]
+                       [bin%-compose
+                        (-> (or/c string? false/c)
+                            (is-a?/c element%) (is-a?/c element%) ...
+                            (or/c (is-a?/c bin%) false/c))]))
 
 (define gst-element-factory (gst 'ElementFactory))
 
@@ -59,9 +66,29 @@
     (and ghost
          (new ghost-pad% [pointer ghost]))))
 
-(define pipeline% (gst 'Pipeline))
+(define gst-bin (gst 'Bin))
+
+(define (bin%-new [name #f])
+  (new bin% [pointer (gst-bin 'new name)]))
+
+(define (bin%-compose name el . els)
+  (let* ([bin (bin%-new name)]
+         [sink el]
+         [source (if (null? els) el (last els))])
+    (and (send/apply bin add-many el els)
+         (when (pair? els)
+           (send/apply el link-many els))
+         (let ([sink-pad (send sink get-static-pad "sink")])
+           (if sink-pad
+               (send bin add-pad (ghost-pad%-new "sink" sink-pad))
+             #t))
+         (let ([source-pad (send source get-static-pad "src")])
+           (if source-pad
+               (send bin add-pad (ghost-pad%-new "src" source-pad))
+             #t))
+         bin)))
 
-(define bin% (gst 'Bin))
+(define pipeline% (gst 'Pipeline))
 
 (define event% (gst 'Event))
 
@@ -70,29 +97,8 @@
 (define (seconds num)
   (* num second))
 
-(define (bin-add-many bin . elements)
-  (for/and ([element elements])
-    (send bin add element)))
-
 (define _input-selector-sync-mode (_enum '(active-segment clock)))
 
-(define (gst-compose name . elements)
-  (let* ([bin (bin% 'new name)]
-         [sink (first elements)]
-         [source (last elements)])
-    (and (> (length elements) 0)
-         (apply bin-add-many bin elements)
-         (apply element-link-many elements)
-         (let ([sink-pad (send sink get-static-pad "sink")])
-           (if sink-pad
-               (send bin add-pad (ghost-pad% 'new "sink" sink-pad))
-               #t))
-         (let ([source-pad (send source get-static-pad "src")])
-           (if source-pad
-               (send bin add-pad (ghost-pad% 'new "src" source-pad))
-               #t))
-         bin)))
-
 (define _video-test-src-pattern (_enum '(smpte
                                          snow black white red green blue
                                          checkers1 checkers2 checkers4 checkers8