From bf158d90ae655a79b3feb3aa8aeb378fd0f0871f Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Tue, 5 Apr 2022 21:06:29 +0200
Subject: [PATCH] Add empty?/1 on Description, Graph and Dataset

---
 CHANGELOG.md                   |  2 ++
 lib/rdf/dataset.ex             | 10 ++++++++++
 lib/rdf/description.ex         | 10 ++++++++++
 lib/rdf/graph.ex               | 10 ++++++++++
 test/unit/dataset_test.exs     |  6 ++++++
 test/unit/description_test.exs |  5 +++++
 test/unit/graph_test.exs       |  5 +++++
 7 files changed, 48 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a7998ec..b30580d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,8 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 
 - a `RDF.Graph` builder DSL available under the `RDF.Graph.build/2` function
 - `RDF.Graph.new/2` and `RDF.Graph.add/2` support the addition of `RDF.Dataset`s
+- `RDF.Description.empty?/1`, `RDF.Graph.empty?/1` and `RDF.Dataset.empty?/1` which
+   are significantly faster than `Enum.empty?/1` 
 - new guards in `RDF.Guards`: `is_statement/1` and `is_quad/1`
 - `RDF.PropertyMap.terms/1` and `RDF.PropertyMap.iris/1`
 
diff --git a/lib/rdf/dataset.ex b/lib/rdf/dataset.ex
index 6ec6b70..54c5bee 100644
--- a/lib/rdf/dataset.ex
+++ b/lib/rdf/dataset.ex
@@ -656,6 +656,16 @@ defmodule RDF.Dataset do
     end)
   end
 
+  @doc """
+  Returns if the given `dataset` is empty.
+
+  Note: You should always prefer this over the use of `Enum.empty?/1` as it is significantly faster.
+  """
+  @spec empty?(t) :: boolean
+  def empty?(%__MODULE__{} = dataset) do
+    Enum.empty?(dataset.graphs) or dataset |> graphs() |> Enum.all?(&Graph.empty?/1)
+  end
+
   @doc """
   Checks if the given `input` statements exist within `dataset`.
 
diff --git a/lib/rdf/description.ex b/lib/rdf/description.ex
index 724ead8..ab10ffc 100644
--- a/lib/rdf/description.ex
+++ b/lib/rdf/description.ex
@@ -637,6 +637,16 @@ defmodule RDF.Description do
 
   defdelegate count(description), to: __MODULE__, as: :statement_count
 
+  @doc """
+  Returns if the given `description` is empty.
+
+  Note: You should always prefer this over the use of `Enum.empty?/1` as it is significantly faster.
+  """
+  @spec empty?(t) :: boolean
+  def empty?(%__MODULE__{} = description) do
+    Enum.empty?(description.predications)
+  end
+
   @doc """
   Checks if the given `input` statements exist within `description`.
   """
diff --git a/lib/rdf/graph.ex b/lib/rdf/graph.ex
index 838b9f9..dea1f54 100644
--- a/lib/rdf/graph.ex
+++ b/lib/rdf/graph.ex
@@ -928,6 +928,16 @@ defmodule RDF.Graph do
 
   defdelegate statements(graph, opts \\ []), to: __MODULE__, as: :triples
 
+  @doc """
+  Returns if the given `graph` is empty.
+
+  Note: You should always prefer this over the use of `Enum.empty?/1` as it is significantly faster.
+  """
+  @spec empty?(t) :: boolean
+  def empty?(%__MODULE__{} = graph) do
+    Enum.empty?(graph.descriptions)
+  end
+
   @doc """
   Checks if the given `input` statements exist within `graph`.
   """
diff --git a/test/unit/dataset_test.exs b/test/unit/dataset_test.exs
index 0be6d33..ca39229 100644
--- a/test/unit/dataset_test.exs
+++ b/test/unit/dataset_test.exs
@@ -1621,6 +1621,12 @@ defmodule RDF.DatasetTest do
     assert Dataset.statement_count(Dataset.new(statement())) == 1
   end
 
+  test "empty?/1" do
+    assert Dataset.empty?(dataset()) == true
+    assert Dataset.empty?(Dataset.new(statement())) == false
+    assert Dataset.empty?(Dataset.new(graph())) == true
+  end
+
   describe "include?/3" do
     test "valid cases" do
       dataset =
diff --git a/test/unit/description_test.exs b/test/unit/description_test.exs
index cafa3b2..25cc90d 100644
--- a/test/unit/description_test.exs
+++ b/test/unit/description_test.exs
@@ -792,6 +792,11 @@ defmodule RDF.DescriptionTest do
     assert Description.statement_count(description({EX.p(), EX.O})) == 1
   end
 
+  test "empty?/1" do
+    assert Description.empty?(Description.new(EX.S)) == true
+    assert Description.empty?(description({EX.p(), EX.O})) == false
+  end
+
   describe "include?/3" do
     test "valid cases" do
       desc =
diff --git a/test/unit/graph_test.exs b/test/unit/graph_test.exs
index 246d92e..2675acc 100644
--- a/test/unit/graph_test.exs
+++ b/test/unit/graph_test.exs
@@ -1288,6 +1288,11 @@ defmodule RDF.GraphTest do
     assert Graph.statement_count(Graph.new(statement())) == 1
   end
 
+  test "empty?/1" do
+    assert Graph.empty?(graph()) == true
+    assert Graph.empty?(Graph.new(statement())) == false
+  end
+
   describe "include?/3" do
     test "valid cases" do
       graph =