...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
There are a few concept archetypes available:
std_real_concept
is an archetype
for theReal types, including the built-in float, double, long double.
#include <boost/concepts/std_real_concept.hpp>
namespace boost{ namespace math{ namespace concepts { class std_real_concept; } }} // namespaces
The main purpose in providing this type is to verify that standard library functions are found via a using declaration - bringing those functions into the current scope - and not just because they happen to be in global scope.
In order to ensure that a call to say pow
can be found either via argument dependent lookup, or failing that then in
the std namespace: all calls to standard library functions are unqualified,
with the std:: versions found via a using
declaration to make them visible in the current scope. Unfortunately it's
all to easy to forget the using
declaration, and call the double version of the function that happens to
be in the global scope by mistake.
For example if the code calls ::pow rather than std::pow, the code will cleanly compile, but truncation of long doubles to double will cause a significant loss of precision. In contrast a template instantiated with std_real_concept will only compile if the all the standard library functions used have been brought into the current scope with a using declaration.
There is a test program libs/math/test/std_real_concept_check.cpp
that instantiates every template in this library with type std_real_concept
to verify its usage of
standard library functions.
#include <boost/math/concepts/real_concept.hpp>
namespace boost{ namespace math{ namespace concepts{ class real_concept; }}} // namespaces
real_concept
is an archetype
for user defined real types,
it declares its standard library functions in its own namespace: these will
only be found if they are called unqualified allowing argument dependent
lookup to locate them. In addition this type is useable at runtime: this
allows code that would not otherwise be exercised by the built-in floating
point types to be tested. There is no std::numeric_limits<> support
for this type, since numeric_limits is not a conceptual requirement for
RealTypes.
NTL RR is an example of a type meeting the requirements that this type models, but note that use of a thin wrapper class is required: refer to "Using With NTL - a High-Precision Floating-Point Library".
There is no specific test case for type real_concept
,
instead, since this type is usable at runtime, each individual test case
as well as testing float
, double
and long
double
, also tests real_concept
.
Distribution Concept models statistical distributions.
#include <boost/math/concepts/distribution.hpp>
namespace boost{ namespace math{ namespace concepts { template <class RealType> class distribution_archetype; template <class Distribution> struct DistributionConcept; }}} // namespaces
The class template distribution_archetype
is a model of the Distribution
concept.
The class template DistributionConcept
is a concept checking
class for distribution types.
The test program distribution_concept_check.cpp
is responsible for using DistributionConcept
to verify that all the distributions in this library conform to the Distribution concept.
The class template DistributionConcept
verifies the existence (but not proper function) of the non-member accessors
required by the Distribution
concept. These are checked by calls like
v = pdf(dist, x); // (Result v is ignored).
And in addition, those that accept two arguments do the right thing when the arguments are of different types (the result type is always the same as the distribution's value_type). (This is implemented by some additional forwarding-functions in derived_accessors.hpp, so that there is no need for any code changes. Likewise boilerplate versions of the hazard/chf/coefficient_of_variation functions are implemented in there too.)