Add ObjectArgument::num_objects

crates/fj-kernel/src/builder/mod.rs

@@ -47,6 +47,9 @@ pub trait ObjectArgument<T>: IntoIterator<Item = T> {
     /// A return value that has one more element thatn the argument
     type SizePlusOne<R>;
 
+    /// Return the number of objects
+    fn num_objects(&self) -> usize;
+
     /// Create a return value by mapping the implementing type
     fn map<F, R>(self, f: F) -> Self::SameSize<R>
     where
@@ -62,6 +65,10 @@ impl<T> ObjectArgument<T> for Vec<T> {
     type SameSize<R> = Vec<R>;
     type SizePlusOne<R> = Vec<R>;
 
+    fn num_objects(&self) -> usize {
+        self.len()
+    }
+
     fn map<F, R>(self, mut f: F) -> Self::SameSize<R>
     where
         F: FnMut(T) -> R,
@@ -96,6 +103,10 @@ macro_rules! impl_object_argument_for_arrays {
                 type SameSize<R> = [R; $len];
                 type SizePlusOne<R> = [R; $len_plus_one];
 
+                fn num_objects(&self) -> usize {
+                    self.len()
+                }
+
                 fn map<F, R>(self, f: F) -> Self::SameSize<R>
                 where
                     F: FnMut(T) -> R,