A C++17 compile time lookup table single header library

This library solves static mapping of keys to values in compile time, allowing for highly optimized code, yet short and concise.

Example

Basic usage

#include <cmap.hpp>

using cmap::make_lookup;
using cmap::map;

// Mapping of int -> int
constexpr auto lookup       = make_lookup(map(12,42), map(13,43));
constexpr auto fourty_two   = lookup[12];
constexpr auto fourty_three = lookup[13];

// Trying to access a bad index will trigger a compiler error
constexpr auto compiler_error = lookup[14];
// error: expression ‘<throw-expression>’ is not a constant expression

// On the other hand, using non constexpr variables an exception is thrown instead
const auto exception_thrown = lookup[14];
// throws std::out_of_range

// Do whatever you want with the lookup result
char data[ lookup[12] ]; // char data[42];

Custom types

#include <cmap.hpp>

using cmap::make_lookup;
using cmap::map;

struct mytype {
  // Equality comparison operator required!
  constexpr bool operator==(const mytype& other) const {
    return value == other.value;
  }
  const int value;
};

constexpr auto lookup_a     = make_lookup(map(mytype{12},42), map(mytype{13},43));
constexpr auto fourty_two   = lookup_a[mytype{12}];
constexpr auto fourty_three = lookup_a[mytype{13}];

constexpr auto lookup_b     = make_lookup(map(42,mytype{12}), map(43,mytype{13}));
constexpr mytype twelve     = lookup_b[42];
constexpr mytype thirteen   = lookup_b[43];

Joining several maps

#include <cmap.hpp>

using cmap::make_lookup;
using cmap::map;

constexpr auto lookup_one = make_lookup(map(12,42), map(13,43));
constexpr auto lookup_two = make_lookup(map(14,44), map(15,45));
constexpr auto lookup     = make_lookup(lookup_one, lookup_two);

constexpr auto fourty_two   = lookup[12];
constexpr auto fourty_three = lookup[13];
constexpr auto fourty_four  = lookup[14];
constexpr auto fourty_five  = lookup[15];

Nested maps

#include <cmap.hpp>

using cmap::make_lookup;
using cmap::map;

constexpr auto lookup = make_lookup(
  map('A', make_lookup(
    map(12, 42),
    map(13, 43)
  )),
  map('B', make_lookup(
    map(14, 44),
    map(15, 45)
  ))
);

constexpr auto fourty_two   = lookup['A'][12];
constexpr auto fourty_three = lookup['A'][13];
constexpr auto fourty_four  = lookup['B'][14];
constexpr auto fourty_five  = lookup['B'][15];

Functional API

#include <cmap.hpp>

using cmap::make_map;
using cmap::lookup;
using cmap::map;

constexpr auto config = make_map(map(12,42), map(13,43));
const auto char my_array[ lookup(config, 12) ]; // Array with 42 elements

Installation

Simply #include <cmap.hpp>.

Running the tests

Make sure you have a C++17 compiler (preferably gcc 7) and cmake >= 3.7 installed. Additionally, for the performance tests you'll need Boost.System.

$ git clone https://github.com/simonvpe/cmap.git
$ cd cmap && mkdir build && cd build && cmake .. && make && ./test/tests

Built With

• gcc 7.0.1
• cmake 3.8

Authors

• Simon Pettersson

License

This project is licensed under the MIT License - see the LICENSE file for details