2571

Reorganize layers in preparation for a better way to manage heap
allocations without ever risking use-after-free errors.

1 files changed, 57 insertions, 0 deletions

diff --git a/044space_surround.cc b/044space_surround.cc
new file mode 100644
index 00000000..821066cc
--- /dev/null
+++ b/044space_surround.cc
@@ -0,0 +1,57 @@
+//: So far you can have global variables by not setting default-space, and
+//: local variables by setting default-space. You can isolate variables
+//: between those extremes by creating 'surrounding' spaces.
+//:
+//: (Surrounding spaces are like lexical scopes in other languages.)
+
+:(scenario surrounding_space)
+# location 1 in space 1 refers to the space surrounding the default space, here 20.
+recipe main [
+  10:number <- copy 5  # pretend array
+  20:number <- copy 5  # pretend array
+  default-space:address:array:location <- copy 10/unsafe
+  0:address:array:location/names:dummy <- copy 20/unsafe  # later layers will explain the /names: property
+  1:number <- copy 32
+  1:number/space:1 <- copy 33
+]
+recipe dummy [
+]
+# chain space
++mem: storing 20 in location 11
+# store to default-space
++mem: storing 32 in location 12
+# store to chained space
++mem: storing 33 in location 22
+
+//: If you think of a space as a collection of variables with a common
+//: lifetime, surrounding allows managing shorter lifetimes inside a longer
+//: one.
+
+:(replace{} "long long int space_base(const reagent& x)")
+long long int space_base(const reagent& x) {
+  return space_base(x, space_index(x), current_call().default_space);
+}
+
+long long int space_base(const reagent& x, long long int space_index, long long int base) {
+  if (space_index == 0) {
+    return base;
+  }
+  long long int result = space_base(x, space_index-1, get_or_insert(Memory, base+1));
+  return result;
+}
+
+long long int space_index(const reagent& x) {
+  for (long long int i = /*skip name:type*/1; i < SIZE(x.properties); ++i) {
+    if (x.properties.at(i).first == "space") {
+      if (!x.properties.at(i).second || x.properties.at(i).second->right)
+        raise_error << maybe(current_recipe_name()) << "/space metadata should take exactly one value in " << x.original_string << '\n' << end();
+      return to_integer(x.properties.at(i).second->value);
+    }
+  }
+  return 0;
+}
+
+:(scenario permit_space_as_variable_name)
+recipe main [
+  space:number <- copy 0
+]