From 4758dac21881cae6f1c7ff6e2257ef63c7eeb402 Mon Sep 17 00:00:00 2001
From: Michel Hermier <michel.hermier@gmail.com>
Date: Wed, 22 Dec 2021 00:34:05 +0100
Subject: [PATCH] AK: Make `Disjoint*::is_empty()` not call size

This is a raffinement of 49cbd4dcca037336ad5e2e4fcb1e3cc613b46cce.

Previously, the container was scanned to compute the size in the unhappy
path. Now, using `all_of` happy and unhappy path should be fast.
---
 AK/DisjointChunks.h             | 11 +++++++++--
 Tests/AK/TestDisjointChunks.cpp |  3 +++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/AK/DisjointChunks.h b/AK/DisjointChunks.h
index d58ed43f7e..181ab1b88a 100644
--- a/AK/DisjointChunks.h
+++ b/AK/DisjointChunks.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/AllOf.h>
 #include <AK/Forward.h>
 #include <AK/Span.h>
 #include <AK/StdLibExtras.h>
@@ -124,7 +125,10 @@ public:
         return size;
     }
 
-    bool is_empty() const { return size() == 0; }
+    bool is_empty() const
+    {
+        return all_of(m_spans, [](auto& span) { return span.is_empty(); });
+    }
 
     DisjointSpans slice(size_t start, size_t length) const
     {
@@ -256,7 +260,10 @@ public:
         return sum;
     }
 
-    bool is_empty() const { return m_chunks.size() == 0 || size() == 0; }
+    bool is_empty() const
+    {
+        return all_of(m_chunks, [](auto& chunk) { return chunk.is_empty(); });
+    }
 
     DisjointSpans<T> spans() const&
     {
diff --git a/Tests/AK/TestDisjointChunks.cpp b/Tests/AK/TestDisjointChunks.cpp
index e8897d2a15..94f052bf9e 100644
--- a/Tests/AK/TestDisjointChunks.cpp
+++ b/Tests/AK/TestDisjointChunks.cpp
@@ -13,8 +13,11 @@
 TEST_CASE(basic)
 {
     DisjointChunks<size_t> chunks;
+    EXPECT(chunks.is_empty());
     chunks.append({});
+    EXPECT(chunks.is_empty());
     chunks.last_chunk().append(0);
+    EXPECT(!chunks.is_empty());
     chunks.append({});
     chunks.last_chunk().append(1);
     chunks.last_chunk().append(2);