[libc-commits] [libc] [libc][wctype] Upstream custom slice implementation from PtrHash-cc prototype to LLVM libc (PR #174779)

[Muhammad Bassiouni via libc-commits]

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+//===-- Internal utils for wctype conversion code - slice -------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// Similar to cpp::span with additional functionality
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_WCTYPE_CONVERSION_UTILS_SLICE_H
+#define LLVM_LIBC_SRC___SUPPORT_WCTYPE_CONVERSION_UTILS_SLICE_H
+
+#include "hdr/types/size_t.h"
+#include "src/__support/CPP/algorithm.h"
+#include "src/__support/CPP/expected.h"
+#include "src/__support/CPP/span.h"
+#include "src/__support/libc_assert.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace wctype_internal {
+
+namespace conversion_utils {
+
+enum class Ordering {
+  /// An ordering where a compared value is less than another.
+  Less = -1,
+  /// An ordering where a compared value is equal to another.
+  Equal = 0,
+  /// An ordering where a compared value is greater than another.
+  Greater = 1,
+};
+
+template <typename T> struct Slice : public cpp::span<T> {
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bassiounix wrote:

> (and `cpp::span` doesn't have a virtual destructor anyways, which probably won't be an issue in your use case, but still)

A span class by design does not own the underlying data, so it has no business managing the underlying memory. 

> looks like this class doesn't provide much utility over `cpp::span`...Why not just implement contains and binary_search_by as freestanding functions that take in a `cpp::span`?

This `Slice` class aims to mimic Rust's slice by interface and internal implementation, also it's meant to be used only here within the internal conversion scope, I have to plans for making this publicly available implementation to be used project-wide.

> Or better, why not just implement generic versions in `libc/src/__support/CPP/algorithm.h`?

I don't think what I'm doing is part of the algorithm header in C++. Given the above and the limited scope of this, I think it's fine to leave it as is.

https://github.com/llvm/llvm-project/pull/174779