13 Templates [temp]

13.8 Name resolution [temp.res]

13.8.3 Dependent names [temp.dep]

13.8.3.4 Value-dependent expressions [temp.dep.constexpr]

1
#
Except as described below, an expression used in a context where a constant expression is required is value-dependent if any subexpression is value-dependent.
2
#
An id-expression is value-dependent if
  • (2.1)
    it is a concept-id and any of its arguments are dependent,
  • (2.2)
    it is type-dependent,
  • (2.3)
    it is the name of a non-type template parameter,
  • (2.4)
    it names a static data member that is a dependent member of the current instantiation and is not initialized in a member-declarator,
  • (2.5)
    it names a static member function that is a dependent member of the current instantiation, or
  • (2.6)
    it names a potentially-constant variable ([expr.const]) that is initialized with an expression that is value-dependent.
Expressions of the following form are value-dependent if the unary-expression or expression is type-dependent or the type-id is dependent:
sizeof unary-expression
sizeof ( type-id )
typeid ( expression )
typeid ( type-id )
alignof ( type-id )
[Note 1: 
For the standard library macro offsetof, see [support.types].
— end note]
3
#
Expressions of the following form are value-dependent if either the type-id, simple-type-specifier, or typename-specifier is dependent or the expression or cast-expression is value-dependent or any expression in the expression-list is value-dependent or any assignment-expression in the braced-init-list is value-dependent:
simple-type-specifier ( expression-list )
typename-specifier ( optexpression-list )
simple-type-specifier braced-init-list
typename-specifier braced-init-list
static_cast < type-id > ( expression )
const_cast < type-id > ( expression )
reinterpret_cast < type-id > ( expression )
dynamic_cast < type-id > ( expression )
( type-id ) cast-expression
4
#
Expressions of the following form are value-dependent:
sizeof ... ( identifier )
fold-expression
unless the identifier is a structured binding pack whose initializer is not dependent.
5
#
A noexcept-expression ([expr.unary.noexcept]) is value-dependent if its expression involves a template parameter.
6
#
An expression of the form &qualified-id where the qualified-id names a dependent member of the current instantiation is value-dependent.
An expression of the form &cast-expression is also value-dependent if evaluating cast-expression as a core constant expression succeeds and the result of the evaluation refers to a templated entity that is an object with static or thread storage duration or a member function.