Support divergent list building

1 files changed, 25 insertions, 5 deletions

diff --git a/runtime/src/shed/namespaces/Std/Lists.c b/runtime/src/shed/namespaces/Std/Lists.c
index f4a01a6d..f7fcf0f8 100644
--- a/runtime/src/shed/namespaces/Std/Lists.c
+++ b/runtime/src/shed/namespaces/Std/Lists.c
@@ -6,6 +6,7 @@ struct ShedArrayBuilder {
     struct ShedGcObjectHeader object_header;
     PatioInt capacity;
     PatioInt size;
+    bool is_owner;
     struct ShedArray* array;
 };
 
@@ -31,6 +32,7 @@ ShedObject shed__runtime__namespace__Std__Lists__arrayBuilder(ShedClosurePointer
     array_builder->object_header.mark = 0b110;
     array_builder->capacity = capacity;
     array_builder->size = 0;
+    array_builder->is_owner = true;
     array_builder->array = array;
 
     return (ShedObject) array_builder;
@@ -59,13 +61,32 @@ ShedObject shed__runtime__namespace__Std__Lists__method__ArrayBuilder__size(Shed
 
 ShedObject shed__runtime__namespace__Std__Lists__method__ArrayBuilder__unsafeAdd(ShedClosurePointer closurePointer, ShedObject arg0, ShedObject arg1) {
     struct ShedArrayBuilder* array_builder = (struct ShedArrayBuilder*) arg0;
-    array_builder->array->elements[array_builder->size] = arg1;
+
+    struct ShedArray* array;
+    if (array_builder->is_owner) {
+        array_builder->is_owner = false;
+        array = array_builder->array;
+    } else {
+        array = shed__runtime__gc_alloc(
+            sizeof(struct ShedArray) + sizeof(ShedObject) * array_builder->capacity,
+            0
+        );
+        array->object_header.mark = 0b110;
+        array->size = array_builder->size;
+
+        for (PatioInt element_index = 0; element_index < array_builder->size; element_index++) {
+            array->elements[element_index] = array_builder->array->elements[element_index];
+        }
+    }
+
+    array->elements[array_builder->size] = arg1;
 
     struct ShedArrayBuilder* new_array_builder = shed__runtime__gc_alloc(sizeof(struct ShedArrayBuilder), 0);
     new_array_builder->object_header.mark = 0b110;
     new_array_builder->capacity = array_builder->capacity;
     new_array_builder->size = array_builder->size + 1;
-    new_array_builder->array = array_builder->array;
+    new_array_builder->is_owner = true;
+    new_array_builder->array = array;
 
     return (ShedObject) new_array_builder;
 }
@@ -77,11 +98,10 @@ ShedObject shed__runtime__namespace__Std__Lists__method__ArrayBuilder__unsafeEnl
 
 ShedObject shed__runtime__namespace__Std__Lists__method__ArrayBuilder__build(ShedClosurePointer closurePointer, ShedObject arg0) {
     struct ShedArrayBuilder* array_builder = (struct ShedArrayBuilder*) arg0;
-    if (array_builder->array->size == 0) {
+    if (array_builder->is_owner) {
+        array_builder->is_owner = false;
         array_builder->array->size = array_builder->size;
         return (ShedObject) array_builder->array;
-    } else if (array_builder->size == array_builder->array->size) {
-        return (ShedObject) array_builder->array;
     } else {
         struct ShedArray* array = shed__runtime__gc_alloc(
             sizeof(struct ShedArray) + sizeof(ShedObject) * array_builder->size,