safe-types

Motivation

The developers use many types in programm, but frequently use only the limited set from a language for its representation (like int, float, char, std::string etc). It may cause some problems in runtime.

For example we should implement chess game. In that case you should have some class which represents a square on a board. Each square can be shown with file and rank (e. g. 'e4' - 5-th file and 4-th rank on a board). Ok, let's try to implement it

class Square
{
public:
	explicit Square(const char file_, const int rank_): file {file_}, rank {rank_}
	{}
private:
	char file;
	int rank;
};

It's a pity but the following code is still compilable

	Square correct('e', 4);
	Square incorrect(4, 'e');

We have missed file and rank order and compiler can't do anything about it (it can show warning only).

Ok. let's try to implement different types for each entity in our program

class FileType
{
	public:
	explicit FileType(const char file_): file {file_}
	{}
private:
	char file;
};

class RankType
{
	public:
	explicit RankType(const char rank_): rank {rank_}
	{}
private:
	char rank;
};

class Square
{
public:
	explicit Square(const FileType file_, const RankType rank_): file {file_}, rank {rank_}
	{}
private:
	FileType file;
	RankType rank;
};

int main() {
	Square correct(FileType{'e'}, RankType{4});
	// Square incorrect(RankType{4}, FileType{'e'});
	// error: no matching function for call to ‘Square::Square(RankType, FileType)’
	return 0;
}

It works as expected. But at this stage we have to think about arithmetic and comparing operations with each new type. If we implement each new operators (like +, -, ==, <=, >=, <, >, !=), our code will grown unexpectedly. At this stage many developers prefer first unsafe code.

This library gives the opportunity to implement new type with no much effort

class FileDimension;
using FileType = safe_type::singleton<char, FileDimension>;

class RankDimension;
using FileType = safe_type::singleton<int, RankDimension>;

class Square
//see above

References

• lib catch is used for unit tests https://github.com/catchorg/Catch2
• library chrono (msvc implementation) is used like example for most arithmetic functions
• reply from Jarod42 https://stackoverflow.com/questions/23855712/how-can-a-type-be-removed-from-a-template-parameter-pack is used like example for struct remove