tmp/tmpergjx29e/{from.md → to.md}
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| 1 |
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#### General <a id="expr.prim.id.general">[[expr.prim.id.general]]</a>
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``` bnf
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id-expression:
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unqualified-id
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qualified-id
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```
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An *id-expression* is a restricted form of a *primary-expression*.
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[*Note 1*: An *id-expression* can appear after `.` and `->` operators
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[[expr.ref]]. — *end note*]
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If an *id-expression* E denotes a member M of an anonymous union
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[[class.union.anon]] U:
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- If U is a non-static data member, E refers to M as a member of the
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lookup context of the terminal name of E (after any transformation to
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a class member access expression [[class.mfct.non.static]]).
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\[*Example 1*: `o.x` is interpreted as `o.u.x`, where u names the
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anonymous union member. — *end example*]
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- Otherwise, E is interpreted as a class member access [[expr.ref]] that
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designates the member subobject M of the anonymous union variable for
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U. \[*Note 2*: Under this interpretation, E no longer denotes a
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non-static data member. — *end note*] \[*Example 2*: `N::x` is
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interpreted as `N::u.x`, where u names the anonymous union
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variable. — *end example*]
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An *id-expression* that denotes a non-static data member or implicit
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object member function of a class can only be used:
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- as part of a class member access [[expr.ref]] in which the object
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expression refers to the member’s class[^10] or a class derived from
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that class, or
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- to form a pointer to member [[expr.unary.op]], or
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- if that *id-expression* denotes a non-static data member and it
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appears in an unevaluated operand.
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\[*Example 3*:
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| 39 |
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``` cpp
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struct S {
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| 41 |
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int m;
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};
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int i = sizeof(S::m); // OK
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int j = sizeof(S::m + 42); // OK
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```
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— *end example*]
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For an *id-expression* that denotes an overload set, overload resolution
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is performed to select a unique function [[over.match]], [[over.over]].
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[*Note 3*:
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A program cannot refer to a function with a trailing *requires-clause*
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whose *constraint-expression* is not satisfied, because such functions
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are never selected by overload resolution.
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[*Example 4*:
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``` cpp
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template<typename T> struct A {
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static void f(int) requires false;
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};
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void g() {
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| 66 |
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A<int>::f(0); // error: cannot call f
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| 67 |
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void (*p1)(int) = A<int>::f; // error: cannot take the address of f
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decltype(A<int>::f)* p2 = nullptr; // error: the type decltype(A<int>::f) is invalid
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}
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```
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In each case, the constraints of `f` are not satisfied. In the
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declaration of `p2`, those constraints are required to be satisfied even
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though `f` is an unevaluated operand [[term.unevaluated.operand]].
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— *end example*]
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— *end note*]
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