Constructor.

Synopsis

Declared in <boost/url/grammar/lut_chars.hpp>

template<class Pred>
requires detail::is_pred<Pred>::value &&
        ! std::is_base_of<
            lut_chars, Pred>::value
constexpr
lut_chars(Pred const& pred) noexcept;

Description

This function constructs a character set which has as members, every value of char ch for which the expression pred(ch) returns true.

Example

struct is_digit
{
    constexpr bool
    operator()(char c ) const noexcept
    {
        return c >= '0' && c <= '9';
    }
};

constexpr lut_chars digits( is_digit{} );

Complexity

Linear in pred, or constant if pred(ch) is a constant expression.

Exception Safety

Throws nothing.

Parameters

Name

Description

pred

The function object to use for determining membership in the character set.

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