7 Expressions [expr]

7.2 Properties of expressions [expr.prop]

7.2.3 Context dependence [expr.context]

In some contexts, unevaluated operands appear ([expr.prim.req.simple], [expr.prim.req.compound], [expr.typeid], [expr.sizeof], [expr.unary.noexcept], [expr.reflect], [dcl.type.decltype], [temp.pre], [temp.concept]).

An unevaluated operand is not evaluated.

[Note 1 :

In an unevaluated operand, a non-static class member can be named ([expr.prim.id]) and naming of objects or functions does not, by itself, require that a definition be provided ([basic.def.odr]).

An unevaluated operand is considered a full-expression .

— end note]

In some contexts, an expression only appears for its side effects.

Such an expression is called a discarded-value expression .

The array-to-pointer and function-to-pointer standard conversions are not applied.

The lvalue-to-rvalue conversion is applied if and only if the expression is a glvalue of volatile-qualified type and it is one of the following:

(2.1)
( expression ), where expression is one of these expressions,
(2.2)
id-expression ([expr.prim.id]),
(2.3)
splice-expression ([expr.prim.splice]),
(2.4)
subscripting,
(2.5)
class member access,
(2.6)
indirection,
(2.7)
pointer-to-member operation,
(2.8)
conditional expression where both the second and the third operands are one of these expressions, or
(2.9)
comma expression where the right operand is one of these expressions.

[Note 2 :

Using an overloaded operator causes a function call; the above covers only operators with built-in meaning.

— end note]

The temporary materialization conversion ([conv.rval]) is applied if the (possibly converted) expression is a prvalue of object type.

[Note 3 :

If the original expression is an lvalue of class type, it must have a volatile copy constructor to initialize the temporary object that is the result object of the temporary materialization conversion.

— end note]

The expression is evaluated and its result (if any) is discarded.