Provide a compile-time check for const
-qualified types.
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Detailed Description
- Outline
-
-
- Purpose:
- Provide a compile-time check for
const
-qualified types.
-
- Classes:
bsl::is_const | meta-function for determining const -qualified types |
bsl::is_const_v | the result value of the bsl::is_const meta-function |
- See also:
- Component bslmf_integralconstant
-
- Description:
- This component defines a meta-function,
bsl::is_const
and a template variable bsl::is_const_v
, that represents the result value of the bsl::is_const
meta-function, that may be used to query whether a type is const
-qualified as defined in the C++ standard [basic.type.qualifier].
bsl::is_const
meets the requirements of the is_const
template defined in the C++11 standard [meta.unary.prop].
- Note that the template variable
is_const_v
is defined in the C++17 standard as an inline variable. If the current compiler supports the inline variable C++17 compiler feature, bsl::is_const_v
is defined as an inline constexpr bool
variable. Otherwise, if the compiler supports the variable templates C++14 compiler feature, bsl::is_const_v
is defined as a non-inline constexpr bool
variable. See BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES
and BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
macros in bsls_compilerfeatures component for details.
-
- Usage:
- In this section we show intended use of this component.
-
- Example 1: Verify const Types:
- Suppose that we want to assert whether a particular type is
const
-qualified.
- First, we create two
typedef
s -- a const
-qualified type and an unqualified type: typedef int MyType;
typedef const int MyConstType;
Now, we instantiate the bsl::is_const
template for each of the typedef
s and assert the value
static data member of each instantiation: Note that if the current compiler supports the variable templates C++14 feature then we can re-write the snippet of code above using the bsl::is_const_v
variable as follows: #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
assert(false == bsl::is_const_v<MyType>);
assert(true == bsl::is_const_v<MyConstType>);
#endif