boost::urls::grammar::lut_chars::lut_chars :: Boost Libraries Documentation

# boost::urls::grammar::lut_chars::lut_chars

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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