usingCustomKeys.dox

Using Custom Keys {#customKeys}
============================

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 `absl::Hash` (default hasher)

```cpp
#include <string>

#include <cachemere.h>

struct ComplexKey {
    std::string first;
    std::string second;

    bool operator==(const ComplexKey& other) const {
        return
    }

    /// Override for the type to be hashable by `absl::Hash`.
    template<typename H> friend H AbslHashValue(H h, const ComplexKey& s)
    {
        return H::combine(std::move(h), s.first, s.second);
    }

    /// For use with cachemere::measurement::CapacityDynamicallyAllocated.
    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

```cpp
#include <string>

#include <cachemere.h>

struct ComplexKey {
    std::string first;
    std::string second;

    bool operator==(const ComplexKey& other) const {
        return
    }

    /// For use with cachemere::measurement::CapacityDynamicallyAllocated.
    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>;
```