Boost C++ Libraries

The type of result returned by library functions.

Synopsis

Defined in header <boost/url/error_types.hpp>

template<
    class T>
using result = boost::system::result< T, system::error_code >;

Description

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This alias is no longer supported and should not be used in new code. Please use system::result instead. This alias is included for backwards compatibility with earlier versions of the library. However, it will be removed in future releases, and using it in new code is not recommended. Please use the updated version instead to ensure compatibility with future versions of the library. This is an alias template used as the return type for functions that can either return a container, or fail with an error code. This is a brief synopsis of the type:

Declaration

template < class T >
class result
{
public :
    //
    // Return true if the result contains an error
    //
    constexpr bool has_error() const noexcept;

    //
    // Return the error
    //
    constexpr system::error_code error() const noexcept;

    //
    // Return true if the result contains a value
    //
    constexpr bool has_value() const noexcept;
    constexpr explicit operator bool () const noexcept;

    //
    // Return the value, or throw an exception
    //
    constexpr T& value();
    constexpr T const& value() const;

    // Return the value.
    // Precondition: has_value()==true
    //
    constexpr T& operator*() noexcept;
    constexpr T* operator->() noexcept;
    constexpr T const& operator*() const noexcept;
    constexpr T const* operator->() const noexcept;

    ...more

Usage

Given the function parse_uri with this signature:

system::result< url_view > parse_uri( core::string_view s ) noexcept ;

The following statement captures the value in a variable upon success, otherwise throws:

url_view u = parse_uri( "http://example.com/path/to/file.txt" ).value();

This statement captures the result in a local variable and inspects the error condition:

system::result< url_view > rv = parse_uri( "http://example.com/path/to/file.txt" );

if (! rv )
    std::cout << rv.error();
else
    std::cout << *rv;

Template Parameters

See Also

Convenience header <boost/url.hpp>