On 12 Jan 2016 at 13:55, Steven Watanabe wrote:
Can I quickly check here if that claim is true? Is there a better way
than my example program?
[snip]
If malloc is your biggest concern, try boost::container::flat_map.
Sorry, the problem being solved was likely poorly specified by me.
What the project idea is for is a boost::[container::]static_map which:
1. Like std::array, it is a fixed size after construction.
2. Like std::array, all member functions are constexpr, thus
allowing constexpr use where Key and T allow that.
3. Keys or the number of items cannot be modified, but values can be.
4. The primary use case example is something like this:
// At global scope, allocates no memory whatsoever
static const constexpr static_map map {
{ 5, "apple" },
{ 8, "pear" },
{ 0, "banana" },
...
};
// Works, constexpr "apple"
constexpr const char *what_is_5 = map[5];
// Works
assert(map[5] && !strcmp(map[5], "apple");
// Works
map[5]="orange";
assert(map[5] && !strcmp(map[5], "orange");
// Throws exception as there is no key 6
map[6];
map.at(6);
Does this make more sense? I know this may seem to be too trivially
easy to be worth adding to Boost, but if you've ever seen code where
people embed large automatically generated data sets into C arrays
and then do linear lookups, the proposed static_map is *exactly* for
that use case - and ~O(1) lookup complexity to boot.
Niall
--
ned Productions Limited Consulting
http://www.nedproductions.biz/
http://ie.linkedin.com/in/nialldouglas/
