Concept for a grammar Rule
Synopsis
Declared in <boost/url/grammar/type_traits.hpp>
template<class T>
concept Rule = requires (T t, char const*& it, char const* end)
{
typename T::value_type;
{ t.parse(it, end) } ‐> std::same_as<system::result<typename T::value_type>>;
};Description
This concept is satisfied if T is a valid grammar Rule
A Rule defines an algorithm used to match an input buffer of ASCII characters against a set of syntactical specifications.
Each rule represents either a terminal symbol or a composition in the represented grammar.
The library comes with a set of rules for productions typically found in RFC documents. Rules are not invoked directly; instead, rule variables are used with overloads of parse which provide a convenient, uniform front end.
Exemplar
For best results, it is suggested that all constructors for rules be marked constexpr.
struct Rule
{
struct value_type;
constexpr Rule( Rule const& ) noexcept = default;
auto parse( char const*& it, char const* end ) const -> result< value_type >;
};
// Declare a variable of type Rule for notational convenience
constexpr Rule rule{};Model
-
dec_octet_rule -
delim_rule -
not_empty_rule -
optional_rule -
range_rule -
token_rule -
tuple_rule -
unsigned_rule -
variant_rule