rate.hpp

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#pragma once
 
/// @file userver/utils/statistics/rate.hpp
/// @brief @copybrief utils::statistics::Rate
 
#include <cstdint>
 
#include <fmt/format.h>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils::statistics {
 
/// @ingroup userver_universal
///
/// @brief `Rate` metrics (or "counter" metrics) are metrics that only monotonically
/// increase or are reset to zero on restart. Some monitoring systems give them
/// special treatment with regard to maintaining proper non-negative derivative.
struct Rate {
    using ValueType = std::uint64_t;
 
    ValueType value{0};
 
    inline Rate& operator+=(Rate other) noexcept {
        value += other.value;
        return *this;
    }
 
    explicit operator bool() const noexcept { return value != 0; }
 
    Rate operator-(Rate rhs) const noexcept { return {value - rhs.value}; }
 
    bool operator==(Rate rhs) const noexcept { return value == rhs.value; }
 
    bool operator!=(Rate rhs) const noexcept { return !(*this == rhs); }
 
    bool operator<(Rate rhs) const noexcept { return value < rhs.value; }
 
    bool operator>(Rate rhs) const noexcept { return rhs < *this; }
 
    bool operator<=(Rate rhs) const noexcept { return !(rhs < *this); }
 
    bool operator>=(Rate rhs) const noexcept { return !(*this < rhs); }
 
    bool operator==(std::uint64_t rhs) const noexcept { return value == rhs; }
 
    bool operator!=(std::uint64_t rhs) const noexcept { return value != rhs; }
 
    bool operator<(std::uint64_t rhs) const noexcept { return value < rhs; }
 
    bool operator>(std::uint64_t rhs) const noexcept { return value > rhs; }
 
    bool operator<=(std::uint64_t rhs) const noexcept { return value <= rhs; }
 
    bool operator>=(std::uint64_t rhs) const noexcept { return value >= rhs; }
};
 
inline Rate operator+(Rate first, Rate second) noexcept { return Rate{first.value + second.value}; }
 
}  // namespace utils::statistics
 
USERVER_NAMESPACE_END
 
template <>
class fmt::formatter<USERVER_NAMESPACE::utils::statistics::Rate> {
public:
    constexpr auto parse(format_parse_context& ctx) { return ctx.begin(); }
 
    template <typename FormatCtx>
    auto format(const USERVER_NAMESPACE::utils::statistics::Rate& rate, FormatCtx& ctx) const {
        return fmt::format_to(ctx.out(), "{}", rate.value);
    }
};