Component bslstl_iserrorconditionenum [Package bslstl]

Provide a compliant standard is_error_condition_enum trait. More...

Outline

• Purpose
• Classes
• Macros
• Description
  • Usage
    • Example 1: Dedicated Error Values

Purpose:

Provide a compliant standard is_error_condition_enum trait.

Classes:

bsl::is_error_condition_enum

standard complaint is_error_condition_enum

Macros:

BSL_IS_ERROR_CONDITION_ENUM_NAMESPACE

namespace to specialize the triat

Canonical Header:

bsl_system_error.h

Description:

This component defines a class template, bsl::is_error_condition_enum, intended to be specialized for enumeration types that are designated as error conditions for the <system_error> facility. In C++11 mode, the vendor-supplied <system_error> implementation is used instead, and the corresponding names from std are imported into bsl. This component also defines a macro, BSL_IS_ERROR_CONDITION_ENUM_NAMESPACE, to be used as the namespace in which to write specializations of is_error_condition_enum.

Usage:

In this section we show intended use of this component.

Example 1: Dedicated Error Values:

Suppose we have a dedicated system with a set of possible errors, and we want to be able to throw descriptive exceptions when an error occurs. We need to work with the <system_error> facility to support this, starting by marking the enumeration type that defines the error literals as eligible to participate. We can use bsl::is_error_condition to do this.

First, we define the set of error values for our system.

  struct CarError {
      // TYPES
      enum Enum {
          k_CAR_WHEELS_CAME_OFF = 1,
          k_CAR_ENGINE_FELL_OUT = 2
      };
  };

Then, we enable the trait marking this as an error condition.

  namespace BSL_IS_ERROR_CONDITION_ENUM_NAMESPACE {
  template <> struct is_error_condition_enum<CarError::Enum>
  : public true_type { };
  }  // close namespace BSL_IS_ERROR_CONDITION_ENUM_NAMESPACE

Finally, we verify that the trait marks our type as eligible.

  assert(is_error_condition_enum<CarError::Enum>::value);