Class template error_code_checker

boost::scope::error_code_checker — A predicate for checking whether an error code indicates error.

Synopsis

// In header: <boost/scope/error_code_checker.hpp>

template<typename ErrorCode> 
class error_code_checker {
public:
  // types
  typedef bool result_type;  // Predicate result type. 

  // construct/copy/destruct
  explicit error_code_checker(ErrorCode &) noexcept;

  // public member functions
  result_type operator()() const noexcept;
};

Description

The predicate captures a reference to an external error code object, which it tests for an error indication when called. The error code object must remain valid for the whole lifetime duration of the predicate.

For an error code object ec, an expression !ec must be valid, never throw exceptions, and return a value contextually convertible to bool. If the returned value converts to false, then this is taken as an error indication, and the predicate returns true. Otherwise, the predicate returns false.

A few examples of error code types:

std::error_code or boost::system::error_code,
std::expected, boost::outcome_v2::basic_outcome or boost::outcome_v2::basic_result,
int, where the value of 0 indicates no error,
bool, where the value of false indicates no error,
T*, where a null pointer indicates no error.

Template Parameters

```
typename ErrorCode
```
Error code type.

`error_code_checker` public construct/copy/destruct

```
explicit error_code_checker(ErrorCode & ec) noexcept;
```
Constructs the predicate.
Upon construction, the predicate saves a reference to the external error code object. The referenced object must remain valid for the whole lifetime duration of the predicate.

Throws: Nothing.

`error_code_checker` public member functions

```
result_type operator()() const noexcept;
```
Checks if the error code indicates error.
Throws: Nothing.

Returns:

As if !!ec, where ec is the error code object passed to the predicate constructor.

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