optional_utility

Header only, boost::optional 's utilities.

Features

• Boost Range Adaptors-like interfaces; map, flat map and filter
• Adaptors are lazy evaluation
• You can use member functions intead of lambda functions
• Non-member functions, value, value_or and value_or_eval
• Non-member function, value_or_throw. This throws exception you pass if boost::optional is boost::none;

Install

Just add the optional_utility.hpp to your build tree.

Dependencies (Requires)

• C++11 or newer
  • You need to define OPTIONAL_UTILITY_NO_CXX14_RETURN_TYPE_DEDUCTION macro if you compile c++11 mode. e.g. -std=c++11
• boost-1.56.0 or newer

Tested Compilers

• gcc
  • 4.9.0 (all of 11, 1y)
  • 4.9.1 (all of 11, 1y)
  • 4.9.2 (all of 11, 1y)
  • 5.1.0 (all of 11, 14, 1z)
  • 5.2.0 (all of 11, 14, 1z)
• clang
  • 3.4 (all of 11, 1y)
  • 3.5 (all of 11, 14, 1z)
• msvc
  • 14.0

gcc and clang was tested on Wandbox

Usage Example

(In all of the examples, assume that threre are appropriate using directives or using namespaces)

• Join adaptors to another using operator|. <optional_value> | <adaptor>(<function>) | ...

• map

optional<int> op = 42;
optional<int> result = op
    | map([](int i) { return i * 2; }); // result is 84

• flat_map

optional<int> op = 42;
optional<int> result = op
    | flat_map([](int i) { return i % 2 ? make_optional(i) : none; }); // result is 42

• filter

optional<int> op = 42;
optional<int> result = op
    | map([](int i) { return i + 1; })
    | filter([](int i) { return i % 2; }); // result is none

• You can use to_optional if you want to convert to optional explicitly

optional<int> op = 42;
optional<int> result;
result = op
    | map([](int i) { return -i; })
    | to_optional; // result is -42

• It can not assign

optional<int> op = 42;
optional<int> result;
result = op
    | map([](int i) { return -i; }); // error

• You can use member function pointers

optional<string> op = "hello"s;
optional<string::size_type> result = op
    | map(&string::length); // result is 5

• You can pass arguments

optional<string> op = "hello"s;
optional<std::string> result = op
    | map(&string::substr, 1, 3); // result is "ell"

Customize

If you define #define OPTIONAL_UTILITY_NAMESPACE op, optional_utilitiy's namespace is op. (default is optional_utility)

TODO

• Enough tests
• The End of adaptors; value, value_or, value_or_eval and value_or_throw