0ffe336887
In a later commit, this concept will be used in a place that's not dependent on trie traversal routines. So extract it to its own header.
40 lines
1.4 KiB
C++
40 lines
1.4 KiB
C++
/*
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* Copyright (C) 2024-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*/
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#pragma once
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#include <concepts>
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#include <iterator>
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#include <span>
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template <typename T>
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concept bytespan_ref = std::same_as<T, std::span<std::byte>&&>
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|| std::same_as<T, std::span<const std::byte>&&>;
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// Converting keys from the regular Scylla format to the BTI byte-comparable format
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// can be expensive, so we allow the conversion to happen lazily.
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// To support that, the traversal routines take the key as an iterator/generator
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// of fragments (byte spans).
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//
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// Note: a std::generator<const_bytes>::iterator fulfils this concept.
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template <typename T>
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concept comparable_bytes_iterator = requires (T it) {
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// Users of comparable_bytes_iterator want to modify the contents of `*it`
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// (for their convenience, not due to necessity), so operator* returns a reference.
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{ *it } -> bytespan_ref;
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// Allowed to destroy `*it`;
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{ ++it };
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// Since this concept is designed for lazy evaluation,
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// the "end" of the sequence is usually more naturally encoded
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// as something in the iterator itself, rather than some external "end" object.
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//
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// So we don't bother with iterator pairs and we instead
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// require the iterator itself to know if it's done.
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{ it == std::default_sentinel } -> std::same_as<bool>;
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{ it != std::default_sentinel } -> std::same_as<bool>;
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}; |