constant
A helper class for templates that require constants and classes that declare value and value_type members.
The class allows constants to be wrapped in a template that defines value and value_type.
This can be particularly useful in recursively defined templates where the value is defined as either a constant or a
further invocation of the template.
Example
Take the example of etl::sqrt.
template <const intmax_t VALUE, const intmax_t I = 1>
struct sqrt
{
typedef typename etl::conditional<((I * I) < VALUE),
etl::sqrt<VALUE, I + 1>,
etl::constant<intmax_t, I> >::type type;
enum value_type
{
value = type::value
};
};
.
template <const intmax_t I>
struct sqrt<I, I>
{
enum value_type
{
value = I
};
};
etl::conditional will select one of the two types based on the boolean template parameter. The types are expected
to have a value member. This is achieved for the constant by wrapping it in etl::constant.