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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/vespalib/util/alloc.h>
#include <vespa/vespalib/util/array.h>
namespace vespalib {
/**
* This is a class that lets you allocate memory tightly. It uses an vector interface
* for storing objects of the same type efficiently. It also providex vector like access with [].
* New objects are just appended to the backing vector, or if there are holes they are inserted there.
* freed objects are not destructed upon free, but rather when the place is required again.
* That happens either
* - on free if it is the last element in the backing vector.
* - when the AllocInArray goes out of scope.
* - on an explicit clear.
**/
template <typename T, typename V=vespalib::Array<T> >
class AllocInArray {
public:
typedef uint32_t Index;
void reserve(size_t sz) { _v.reserve(sz); }
Index alloc(const T & v);
void free(Index p);
const T & operator [] (Index p) const { return _v[p]; }
T & operator [] (Index p) { return _v[p]; }
void clear();
size_t size() const { return _v.size() - _free.size(); }
private:
Index last() const { return _v.size() - 1; }
typedef vespalib::Array<Index> FreeList;
V _v;
FreeList _free;
};
template <typename T, typename V>
typename AllocInArray<T, V>::Index
AllocInArray<T, V>::alloc(const T & v)
{
if (_free.empty()) {
_v.push_back(v);
return last();
} else {
Index p(_free.back());
_free.pop_back();
_v[p] = v;
return p;
}
}
template <typename T, typename V>
void
AllocInArray<T, V>::free(Index p)
{
if (p == last()) {
_v.pop_back();
} else if ( p < _v.size()) {
_free.push_back(p);
}
}
template <typename T, typename V>
void
AllocInArray<T, V>::clear()
{
_v.clear();
_free.clear();
}
}
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