explicit

A set of small tools that allow you to state your intentions more explicitly in the interfaces.

Tool out_param

A tool for indicating function output parameters in call sites:

void clear(out_param<std::string&> s) // output parameter in function declaration
{
    s.get().clear();
}

std::string s {"text"};
clear(out(s));                        // in function invokation

For more, see here.

Tool tagged_bool

An alternative to type bool in function arguments. It allows to associate a name with the boolean type. No nasty implicit converisons from/to int, double, or pointers. Different instantiations of tagged_bool are not interconvertible:

using EngineStarted = tagged_bool<class EngineStartedTag>; // one boolean type
using CrewReady     = tagged_bool<class CrewReadyTag>;     // another boolean type

void set_status(EngineStarted started, CrewReady ready); // function declaration
set_status(EngineStarted{true}, CrewReady{true});        // function invokation

For more, see here.

Tool only_when

A tool for disabling some unwanted implicit conversions to types present in your function signatures. For instance, you may want your function to take a filesystem::path but not allow an implicit conversion from std::string:

using only_path = only_when<filesystem::path, is_a_non_string>; // you define type trait is_a_non_string
void process(only_path p);  // function declaration
process(path);    // ok
process(string);  // error

For more, see here.

Tool only_int

An alternative to type int in function arguments. It binds to ints and int proxies but not to double:

void scale(only_int i); // declaration
scale(2);     // ok
scale(2.5);   // error

For more, see here.

Tool lvalue_ref

This allows the constructor parameters to bind to lvalues, but not to rvalues:

struct Processor
{
  Big const& _big;
  explicit Processor(lvalue_ref<const Big> b) : _big(b) {}
};

const Big b {};
Processor p {b}; // ok
Processor q {Big{}}; // error (temporary)

For more, see here.

Tool not_null

This allows to indicate in function interface that a passed pointer is assumed never to be null:

void process(not_null<i*> p); // function declaration
int i = 0;
process(&i);                  // error: no implicit conversion to not_null
process(as_not_null(&i));     // ok: explicit adjustment

For more, see here.

installation

It is a C++11 header-only library.

License

Distributed under the Boost Software License, Version 1.0.

Acknowledgements

The idea of the generalized only_when was proposed by Vicente J. Botet Escriba. Tomasz Kamiński suggested the support for std::reference_wrapper in rvalue_ref.