AK: Add format function like std::format or fmt::format.

AK/Format.h

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Array.h>
+#include <AK/String.h>
+
+namespace AK {
+
+template<typename T, typename = void>
+struct Formatter;
+
+} // namespace AK
+
+namespace AK::Detail::Format {
+
+template<typename T>
+bool format_value(StringBuilder& builder, const void* value, StringView flags)
+{
+    Formatter<T> formatter;
+
+    if (!formatter.parse(flags))
+        return false;
+
+    formatter.format(builder, *static_cast<const T*>(value));
+    return true;
+}
+
+struct TypeErasedFormatter {
+    bool (*format)(StringBuilder& builder, const void* value, StringView flags);
+    const void* parameter;
+};
+
+template<typename T>
+TypeErasedFormatter make_type_erased_formatter(const T& value) { return { format_value<T>, &value }; }
+
+String format(StringView fmtstr, AK::Span<TypeErasedFormatter>, size_t argument_index = 0);
+void format(StringBuilder&, StringView fmtstr, AK::Span<TypeErasedFormatter>, size_t argument_index = 0);
+
+} // namespace AK::Detail::Format
+
+namespace AK {
+
+template<size_t Size>
+struct Formatter<char[Size]> {
+    bool parse(StringView) { return true; }
+    void format(StringBuilder& builder, const char* value) { builder.append(value); }
+};
+
+template<>
+struct Formatter<StringView> {
+    bool parse(StringView flags) { return flags.is_empty(); }
+    void format(StringBuilder& builder, StringView value) { builder.append(value); }
+};
+template<>
+struct Formatter<String> {
+    bool parse(StringView flags) { return flags.is_empty(); }
+    void format(StringBuilder& builder, const String& value) { builder.append(value); }
+};
+
+template<typename T>
+struct Formatter<T, typename EnableIf<IsIntegral<T>::value>::Type> {
+    bool parse(StringView flags);
+    void format(StringBuilder&, T value);
+
+    bool zero_pad { false };
+    bool hexadecimal { false };
+    size_t field_width { 0 };
+};
+
+template<typename... Parameters>
+String format(StringView fmtstr, const Parameters&... parameters)
+{
+    Array formatters { Detail::Format::make_type_erased_formatter(parameters)... };
+    return Detail::Format::format(fmtstr, formatters);
+}
+
+}