Apply suggestions from code review

Co-authored-by: Jonatan Kłosko <jonatanklosko@gmail.com>

Author: wojtekmach

example/Makefile

@@ -1,15 +1,29 @@
-SRC := c_src/example_nif.cpp
-TARGET := $(MIX_BUILD_DIR)/example_nif.so
+PRIV_DIR := $(MIX_APP_PATH)/priv
+NIF_PATH := $(PRIV_DIR)/libexample.so
+C_SRC := $(shell pwd)/c_src
 
-CPPFLAGS := -std=c++17 -fvisibility=hidden -fPIC -I$(ERL_INCLUDE_DIR) -I$(FINE_INCLUDE_DIR)
+CPPFLAGS := -shared -fPIC -std=c++17 -Wall -Wextra
+CPPFLAGS += -I$(ERTS_INCLUDE_DIR) -I$(FINE_INCLUDE_DIR)
 
-ifeq ($(shell uname -s),Darwin)
-    LDFLAGS := -dynamiclib -undefined dynamic_lookup
+ifdef DEBUG
+	CPPFLAGS += -g
 else
-    LDFLAGS := -shared
+	CPPFLAGS += -O3
 endif
 
-all: $(TARGET)
+ifndef TARGET_ABI
+  TARGET_ABI := $(shell uname -s | tr '[:upper:]' '[:lower:]')
+endif
+
+ifeq ($(TARGET_ABI),darwin)
+	CPPFLAGS += -undefined dynamic_lookup -flat_namespace
+endif
+
+SOURCES := $(wildcard $(C_SRC)/*.cpp)
+
+all: $(NIF_PATH)
+	@ echo > /dev/null # Dummy command to avoid the default output "Nothing to be done"
 
-$(TARGET): $(SRC)
-	$(CXX) $(CPPFLAGS) $(LDFLAGS) -o $@ $^
+$(NIF_PATH): $(SOURCES)
+	@ mkdir -p $(PRIV_DIR)
+	$(CXX) $(CPPFLAGS) $(SOURCES) -o $(NIF_PATH)

example/lib/example.ex

@@ -1,9 +1,13 @@
 defmodule Example do
-  @on_load :load_nif
-  @mix_build_dir Mix.Project.build_path()
+  @on_load :__on_load__
 
-  defp load_nif do
-    :erlang.load_nif(~c"#{@mix_build_dir}/example_nif", 0)
+  def __on_load__ do
+    path = :filename.join(:code.priv_dir(:example), ~c"libexample")
+
+    case :erlang.load_nif(path, 0) do
+      :ok -> :ok
+      {:error, reason} -> raise "failed to load NIF library, reason: #{inspect(reason)}"
+    end
   end
 
   @doc """

example/mix.exs

@@ -7,13 +7,7 @@ defmodule Example.MixProject do
       version: "0.1.0",
       elixir: "~> 1.15",
       compilers: [:elixir_make] ++ Mix.compilers(),
-      make_env: fn ->
-        %{
-          "MIX_BUILD_DIR" => Mix.Project.build_path(),
-          "ERL_INCLUDE_DIR" => "#{:code.root_dir()}/usr/include",
-          "FINE_INCLUDE_DIR" => Fine.include_dir()
-        }
-      end,
+      make_env: fn -> %{"FINE_INCLUDE_DIR" => Fine.include_dir()} end,
       deps: deps()
     ]
   end