specs for aliased containers

SPEC.md

@@ -552,6 +552,39 @@ class Point
 end
 ```
 
+### §2.6 Generic types
+
+Only sequential container types are instantiated on the Crystal side, as if each
+container implements the following interface:
+
+```crystal
+module Container(T)
+  include Indexable(T)
+
+  # All containers must be default-constructible
+  # abstract def initialize
+
+  abstract def unsafe_fetch(index : Int) : T
+  abstract def push(value : T) : Void
+  abstract def size : Int32
+
+  def <<(x : T)
+    push(x)
+    self
+  end
+
+  def concat(values : Enumerable(T))
+    values.each { |v| self << v }
+    self
+  end
+end
+```
+
+Bindgen automatically collects all instantiations of each container type that
+appear in method argument types or return types; explicit instantiations may be
+configured with the `containers` section.  Aliases to complete container types
+and container type arguments are both supported.
+
 ## §3. Crystal bindings
 
 ### §3.1 Naming scheme

spec/integration/containers.cpp

@@ -1,6 +1,9 @@
 #include <vector>
 #include <string>
 
+typedef std::vector<unsigned char> bytearray;
+typedef unsigned int rgb;
+
 class Containers {
 public:
   std::vector<int> integers() {
@@ -15,6 +18,14 @@ class Containers {
     return std::vector<std::string>{ "One", "Two", "Three" };
   }
 
+  bytearray chars() {
+    return { 0x01, 0x04, 0x09 };
+  }
+
+  std::vector<rgb> palette() {
+    return { 0xFF0000, 0x00FF00, 0x0000FF };
+  }
+
   double sum(std::vector<double> list) {
     double d = 0;
 

spec/integration/containers.yml

@@ -2,6 +2,7 @@
 
 processors:
   - filter_methods
+  - auto_container_instantiation
   - instantiate_containers
   - default_constructor
   - cpp_wrapper
@@ -17,6 +18,8 @@ containers:
     type: Sequential
     instantiations:
       - [ "int" ]
-      - [ "double" ]
-      - [ "std::string" ]
       - [ "std::vector<int>" ]
+
+types:
+  rgb: { alias_for: "unsigned int" }
+  bytearray: { alias_for: std::vector<unsigned char> }

spec/integration/containers_spec.cr

@@ -17,6 +17,14 @@ describe "container instantiation feature" do
           Test::Containers.new.sum(list).should eq(4.0)
         end
 
+        it "works with auto instantiated container (aliased container)" do
+          Test::Containers.new.chars.to_a.should eq([1u8, 4u8, 9u8])
+        end
+
+        it "works with auto instantiated container (aliased element)" do
+          Test::Containers.new.palette.to_a.should eq([0xFF0000u32, 0x00FF00u32, 0x0000FFu32])
+        end
+
         it "works with nested containers" do
           Test::Containers.new.grid.to_a.map(&.to_a).should eq([[1, 4], [9, 16]])
         end