Using Custom Keys

This page is meant to guide you through the usage of a custom key with a cache.

Key Requirements

• Must have both a move constructor and a move assignment operator.
• Must implement equality operator (bool operator==(const Self&) const;).
• Must be hashable by the hasher passed as template parameter to the cache (by default, absl::Hash<Key>).

The key does not need to be copyable.

Usage Example

With <tt>absl::Hash</tt> (default hasher)

#include <string>
 
#include <cachemere.h>
 
struct ComplexKey {
    std::string first;
    std::string second;
 
    bool operator==(const ComplexKey& other) const {
        return
    }
 
    template<typename H> friend H AbslHashValue(H h, const ComplexKey& s)
    {
        return H::combine(std::move(h), s.first, s.second);
    }
 
    size_t capacity() const {
        return first.capacity() + second.capacity();
    }
};
 
usig ValueT = int;
 
using Cache = cachemere::presets::memory::LRUCache<ComplexKey,
                                                   ValueT,
                                                   cachemere::measurement::SizeOf,
                                                   cachemere::measurement::CapacityDynamicallyAllocated>;

With a custom hasher

#include <string>
 
#include <cachemere.h>
 
struct ComplexKey {
    std::string first;
    std::string second;
 
    bool operator==(const ComplexKey& other) const {
        return
    }
 
    size_t capacity() const {
        return first.capacity() + second.capacity();
    }
};
 
 
struct VeryBadHash {
    size_t operator(const ComplexKey&) {
        return 0;
    }
};
 
usig ValueT = int;
 
using Cache = cachemere::presets::memory::LRUCache<ComplexKey,
                                                   ValueT,
                                                   cachemere::measurement::SizeOf,
                                                   cachemere::measurement::CapacityDynamicallyAllocated,
                                                   VeryBadHash>;