AK: Add a StringView class.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/461aa550eb8

AK/AKString.h

@@ -1,11 +1,12 @@
 #pragma once
 
-#include "ByteBuffer.h"
-#include "RetainPtr.h"
-#include "StringImpl.h"
-#include "Traits.h"
-#include "Vector.h"
-#include "kstdio.h"
+#include <AK/ByteBuffer.h>
+#include <AK/RetainPtr.h>
+#include <AK/StringImpl.h>
+#include <AK/Traits.h>
+#include <AK/Vector.h>
+#include <AK/StringView.h>
+#include <AK/kstdio.h>
 
 namespace AK {
 
@@ -14,6 +15,12 @@ public:
     ~String() { }
 
     String() { }
+
+    String(StringView view)
+        : m_impl(StringImpl::create(view.characters(), view.length()))
+    {
+    }
+
     String(const String& other)
         : m_impl(const_cast<String&>(other).m_impl.copy_ref())
     {
@@ -111,6 +118,8 @@ public:
 
     static String format(const char*, ...);
 
+    StringView view() const { return { characters(), length() }; }
+
 private:
     RetainPtr<StringImpl> m_impl;
 };

AK/StringView.h

@@ -0,0 +1,25 @@
+#pragma once
+
+class StringView {
+public:
+    StringView() { }
+    StringView(const char* characters, int length) : m_characters(characters), m_length(length) { }
+    StringView(const unsigned char* characters, int length) : m_characters((const char*)characters), m_length(length) { }
+    StringView(const char* cstring)
+        : m_characters(cstring)
+    {
+        if (cstring) {
+            while (*(cstring++))
+                ++m_length;
+        }
+    }
+
+    bool is_empty() const { return m_length == 0; }
+    const char* characters() const { return m_characters; }
+    int length() const { return m_length; }
+    char operator[](int index) const { return m_characters[index]; }
+
+private:
+    const char* m_characters { nullptr };
+    int m_length { 0 };
+};