13 Templates [temp]

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.

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 )
noexcept ( expression )

Expressions of the following form are value-dependent if either the type-id or simple-type-specifier is dependent or the expression or cast-expression is value-dependent:

simple-type-specifier ( expression-list${}_{opt}$ )
static_­cast < type-id > ( expression )
const_­cast < type-id > ( expression )
reinterpret_­cast < type-id > ( expression )
( type-id ) cast-expression

Expressions of the following form are value-dependent:

sizeof ... ( identifier )
fold-expression

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.