cppdraft_translate/cppdraft/meta/reflection/access/queries.md

[meta.reflection.access.queries]

21 Metaprogramming library [meta]

21.4 Reflection [meta.reflection]

21.4.9 Member accessibility queries [meta.reflection.access.queries]

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consteval bool is_accessible(info r, access_context ctx);

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Let PARENT-CLS(r) be:

• (1.1)

  If parent_of(r) represents a class C, then C.

• (1.2)

  Otherwise, PARENT-CLS(parent_of(r)).

2

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Let DESIGNATING-CLS(r, ctx) be:

• (2.1)

  If ctx.designating_class() represents a class C, then C.

• (2.2)

  Otherwise, PARENT-CLS(r).

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Returns:

• (3.1)

  If r represents an unnamed bit-field F, then is_accessible(rH, ctx), where rH represents a hypothetical non-static data member of the class represented by PARENT-CLS(r) with the same access as F. [Note 1: Unnamed bit-fields are treated as class members for the purpose of is_accessible. — end note]

• (3.2)

  Otherwise, if r does not represent a class member or a direct base class relationship, then true.

• (3.3)

  Otherwise, if r represents

  • (3.3.1)

a class member that is not a (possibly indirect or variant) member of DESIGNATING-CLS(​r, ctx) or

• (3.3.2)

a direct base class relationship such that parent_of(r) does not represent DESIGNATING-CLS(​r, ctx) or a (direct or indirect) base class thereof,

then false.

• (3.4)

  Otherwise, if ctx.scope() is the null reflection, then true.

• (3.5)

  Otherwise, letting P be a program point whose immediate scope is the function parameter scope, class scope, or namespace scope corresponding to the function, class, or namespace represented by ctx.scope():

  • (3.5.1)

    If r represents a direct base class relationship (D,B), then true if base class B of DESIGNATING-CLS(​r, ctx) is accessible at P ([class.access.base]); otherwise false.

  • (3.5.2)

    Otherwise, r represents a class member M; true if M would be accessible at P with the designating class ([class.access.base]) as DESIGNATING-CLS(r, ctx) if the effect of any using-declarations ([namespace.udecl]) were ignored. Otherwise, false.

[Note 2:

The definitions of when a class member or base class is accessible from a point P do not consider whether a declaration of that entity is reachable from P.

— end note]

[Example 1: consteval access_context fn() {return access_context::current();}class Cls {int mem; friend consteval access_context fn();public:static constexpr auto r = ^^mem;};

static_assert(is_accessible(Cls::r, fn())); // OKstatic_assert(!is_accessible(Cls::r, access_context::current())); // OKstatic_assert(is_accessible(Cls::r, access_context::unchecked())); // OK — end example]

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Throws: meta​::​exception if

• (4.1)

r represents a class member for which PARENT-CLS(r) is an incomplete class or

• (4.2)

r represents a direct base class relationship (D,B) for which D is incomplete.

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consteval bool has_inaccessible_nonstatic_data_members(info r, access_context ctx);

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Returns: true if is_accessible(R, ctx) is false for any R in nonstatic_data_members_of(​r, access_context​​::​unchecked()).

Otherwise, false.

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Throws: meta​::​exception unless

• (6.1)

nonstatic_data_members_of(​r, access_context​::​​unchecked()) is a constant subexpression and

• (6.2)

r does not represent a closure type.

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consteval bool has_inaccessible_bases(info r, access_context ctx);

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Returns: true if is_accessible(R, ctx) is false for any R in bases_of(​r, access_context​::​​unchecked()).

Otherwise, false.

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Throws: meta​::​exception unlessbases_of(r, access_context​::​unchecked()) is a constant subexpression.

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consteval bool has_inaccessible_subobjects(info r, access_context ctx);

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Effects: Equivalent to:return has_inaccessible_bases(r, ctx) || has_inaccessible_nonstatic_data_members(r, ctx);