Add Rust std::shared_ptr binding
diff --git a/syntax/check.rs b/syntax/check.rs
index 2ebbf05..6dce563 100644
--- a/syntax/check.rs
+++ b/syntax/check.rs
@@ -32,6 +32,7 @@
             Type::RustBox(ptr) => check_type_box(cx, ptr),
             Type::RustVec(ty) => check_type_rust_vec(cx, ty),
             Type::UniquePtr(ptr) => check_type_unique_ptr(cx, ptr),
+            Type::SharedPtr(ptr) => check_type_shared_ptr(cx, ptr),
             Type::CxxVector(ptr) => check_type_cxx_vector(cx, ptr),
             Type::Ref(ty) => check_type_ref(cx, ty),
             Type::Array(array) => check_type_array(cx, array),
@@ -115,6 +116,7 @@
     if let Type::Ident(ident) = &ptr.inner {
         if cx.types.rust.contains(&ident.rust) {
             cx.error(ptr, "unique_ptr of a Rust type is not supported yet");
+            return;
         }
 
         match Atom::from(&ident.rust) {
@@ -128,6 +130,29 @@
     cx.error(ptr, "unsupported unique_ptr target type");
 }
 
+fn check_type_shared_ptr(cx: &mut Check, ptr: &Ty1) {
+    if let Type::Ident(ident) = &ptr.inner {
+        if cx.types.rust.contains(&ident.rust) {
+            cx.error(ptr, "shared_ptr of a Rust type is not supported yet");
+            return;
+        }
+
+        match Atom::from(&ident.rust) {
+            None => return,
+            Some(CxxString) => {
+                cx.error(ptr, "std::shared_ptr<std::string> is not supported yet");
+                return;
+            }
+            _ => {}
+        }
+    } else if let Type::CxxVector(_) = &ptr.inner {
+        cx.error(ptr, "std::shared_ptr<std::vector> is not supported yet");
+        return;
+    }
+
+    cx.error(ptr, "unsupported shared_ptr target type");
+}
+
 fn check_type_cxx_vector(cx: &mut Check, ptr: &Ty1) {
     if let Type::Ident(ident) = &ptr.inner {
         if cx.types.rust.contains(&ident.rust) {
@@ -135,6 +160,7 @@
                 ptr,
                 "C++ vector containing a Rust type is not supported yet",
             );
+            return;
         }
 
         match Atom::from(&ident.rust) {
@@ -410,7 +436,7 @@
         return;
     }
 
-    if let Type::UniquePtr(ty) | Type::CxxVector(ty) = ty {
+    if let Type::UniquePtr(ty) | Type::SharedPtr(ty) | Type::CxxVector(ty) = ty {
         if let Type::Ident(inner) = &ty.inner {
             if Atom::from(&inner.rust).is_none() {
                 return;
@@ -473,6 +499,7 @@
 fn check_reserved_name(cx: &mut Check, ident: &Ident) {
     if ident == "Box"
         || ident == "UniquePtr"
+        || ident == "SharedPtr"
         || ident == "Vec"
         || ident == "CxxVector"
         || ident == "str"
@@ -493,6 +520,7 @@
         Type::RustBox(_)
         | Type::RustVec(_)
         | Type::UniquePtr(_)
+        | Type::SharedPtr(_)
         | Type::Ref(_)
         | Type::Str(_)
         | Type::SliceRef(_) => false,
@@ -564,6 +592,7 @@
         Type::RustBox(_) => "Box".to_owned(),
         Type::RustVec(_) => "Vec".to_owned(),
         Type::UniquePtr(_) => "unique_ptr".to_owned(),
+        Type::SharedPtr(_) => "shared_ptr".to_owned(),
         Type::Ref(_) => "reference".to_owned(),
         Type::Str(_) => "&str".to_owned(),
         Type::CxxVector(_) => "C++ vector".to_owned(),
diff --git a/syntax/error.rs b/syntax/error.rs
index d0ae021..a672329 100644
--- a/syntax/error.rs
+++ b/syntax/error.rs
@@ -29,7 +29,7 @@
 pub static BOX_CXX_TYPE: Error = Error {
     msg: "Box of a C++ type is not supported yet",
     label: None,
-    note: Some("hint: use UniquePtr<>"),
+    note: Some("hint: use UniquePtr<> or SharedPtr<>"),
 };
 
 pub static CXXBRIDGE_RESERVED: Error = Error {
@@ -47,7 +47,7 @@
 pub static CXX_TYPE_BY_VALUE: Error = Error {
     msg: "C++ type by value is not supported",
     label: None,
-    note: Some("hint: wrap it in a UniquePtr<>"),
+    note: Some("hint: wrap it in a UniquePtr<> or SharedPtr<>"),
 };
 
 pub static DISCRIMINANT_OVERFLOW: Error = Error {
diff --git a/syntax/impls.rs b/syntax/impls.rs
index 73cb1d9..9b154f6 100644
--- a/syntax/impls.rs
+++ b/syntax/impls.rs
@@ -45,6 +45,7 @@
             Type::Ident(t) => t.hash(state),
             Type::RustBox(t) => t.hash(state),
             Type::UniquePtr(t) => t.hash(state),
+            Type::SharedPtr(t) => t.hash(state),
             Type::Ref(t) => t.hash(state),
             Type::Str(t) => t.hash(state),
             Type::RustVec(t) => t.hash(state),
@@ -65,6 +66,7 @@
             (Type::Ident(lhs), Type::Ident(rhs)) => lhs == rhs,
             (Type::RustBox(lhs), Type::RustBox(rhs)) => lhs == rhs,
             (Type::UniquePtr(lhs), Type::UniquePtr(rhs)) => lhs == rhs,
+            (Type::SharedPtr(lhs), Type::SharedPtr(rhs)) => lhs == rhs,
             (Type::Ref(lhs), Type::Ref(rhs)) => lhs == rhs,
             (Type::Str(lhs), Type::Str(rhs)) => lhs == rhs,
             (Type::RustVec(lhs), Type::RustVec(rhs)) => lhs == rhs,
diff --git a/syntax/improper.rs b/syntax/improper.rs
index e0e5154..c0f6983 100644
--- a/syntax/improper.rs
+++ b/syntax/improper.rs
@@ -28,7 +28,7 @@
             | Type::Fn(_)
             | Type::Void(_)
             | Type::SliceRef(_) => Definite(true),
-            Type::UniquePtr(_) | Type::CxxVector(_) => Definite(false),
+            Type::UniquePtr(_) | Type::SharedPtr(_) | Type::CxxVector(_) => Definite(false),
             Type::Ref(ty) => self.determine_improper_ctype(&ty.inner),
             Type::Array(ty) => self.determine_improper_ctype(&ty.inner),
         }
diff --git a/syntax/mod.rs b/syntax/mod.rs
index e8bd290..12b269e 100644
--- a/syntax/mod.rs
+++ b/syntax/mod.rs
@@ -167,6 +167,7 @@
     RustBox(Box<Ty1>),
     RustVec(Box<Ty1>),
     UniquePtr(Box<Ty1>),
+    SharedPtr(Box<Ty1>),
     Ref(Box<Ref>),
     Str(Box<Ref>),
     CxxVector(Box<Ty1>),
diff --git a/syntax/parse.rs b/syntax/parse.rs
index a3f50ec..e4f0512 100644
--- a/syntax/parse.rs
+++ b/syntax/parse.rs
@@ -822,6 +822,16 @@
                             rangle: generic.gt_token,
                         })));
                     }
+                } else if ident == "SharedPtr" && generic.args.len() == 1 {
+                    if let GenericArgument::Type(arg) = &generic.args[0] {
+                        let inner = parse_type(arg)?;
+                        return Ok(Type::SharedPtr(Box::new(Ty1 {
+                            name: ident,
+                            langle: generic.lt_token,
+                            inner,
+                            rangle: generic.gt_token,
+                        })));
+                    }
                 } else if ident == "CxxVector" && generic.args.len() == 1 {
                     if let GenericArgument::Type(arg) = &generic.args[0] {
                         let inner = parse_type(arg)?;
diff --git a/syntax/tokens.rs b/syntax/tokens.rs
index edbf818..07738d8 100644
--- a/syntax/tokens.rs
+++ b/syntax/tokens.rs
@@ -20,9 +20,11 @@
                 }
                 ident.rust.to_tokens(tokens);
             }
-            Type::RustBox(ty) | Type::UniquePtr(ty) | Type::CxxVector(ty) | Type::RustVec(ty) => {
-                ty.to_tokens(tokens)
-            }
+            Type::RustBox(ty)
+            | Type::UniquePtr(ty)
+            | Type::SharedPtr(ty)
+            | Type::CxxVector(ty)
+            | Type::RustVec(ty) => ty.to_tokens(tokens),
             Type::Ref(r) | Type::Str(r) => r.to_tokens(tokens),
             Type::Array(a) => a.to_tokens(tokens),
             Type::Fn(f) => f.to_tokens(tokens),
@@ -44,7 +46,7 @@
     fn to_tokens(&self, tokens: &mut TokenStream) {
         let span = self.name.span();
         let name = self.name.to_string();
-        if let "UniquePtr" | "CxxVector" = name.as_str() {
+        if let "UniquePtr" | "SharedPtr" | "CxxVector" = name.as_str() {
             tokens.extend(quote_spanned!(span=> ::cxx::));
         } else if name == "Vec" {
             tokens.extend(quote_spanned!(span=> ::std::vec::));
diff --git a/syntax/types.rs b/syntax/types.rs
index c98fe85..70b381f 100644
--- a/syntax/types.rs
+++ b/syntax/types.rs
@@ -45,6 +45,7 @@
                 Type::Ident(_) | Type::Str(_) | Type::Void(_) => {}
                 Type::RustBox(ty)
                 | Type::UniquePtr(ty)
+                | Type::SharedPtr(ty)
                 | Type::CxxVector(ty)
                 | Type::RustVec(ty) => visit(all, &ty.inner),
                 Type::Ref(r) => visit(all, &r.inner),
@@ -254,7 +255,7 @@
                     Atom::from(&ident.rust) == Some(RustString)
                 }
             }
-            Type::RustVec(_) | Type::Array(_) => true,
+            Type::SharedPtr(_) | Type::RustVec(_) | Type::Array(_) => true,
             _ => false,
         }
     }