2 An object is an immediate object if its complete object has

• (2.0) is the object declared by, or a temporary object whose lifetime is extended to that of, a variable declared with the consteval specifier,
• (2.1) has a constituent value that is consteval-only, or
• (2.2) has a constituent reference that refers to an immediate object or immediate function.

8 For any condition or for-range-declaration D, each decl-specifier in the decl-specifier-seq of D, including that of any structured-binding-declaration of D, shall be either a type-specifier, consteval, or constexpr.

1 Expansion statements specify repeated instantiations ([temp.decls.general]) of their substatement.

Let CONST-SPECIFIER consist of each decl-specifier of the decl-specifier-seq of the for-range-declaration that is either consteval or constexpr.

[…]

• (5.2) Otherwise, if S is an iterating expansion statement, S is equivalent to:

  {
    init-statement
    constexpropt CONST-SPECIFIER decltype(auto) range = ( expansion-initializer );
    constexpropt CONST-SPECIFIER auto begin = begin-expr; // see [stmt.ranged]
  
    S0
    ...
    S$N$-1
  }

  where N is the result of evaluating the expression

  […]

  and Si is

  {
    constexpropt CONST-SPECIFIER auto iter = begin + decltype(begin - begin){i};
    for-range-declaration = *iter;
    compound-statement
  }

  The variables range, begin, and iter are defined for exposition only. The keyword constexpr is present in the declarations of range, begin, and iter if and only if constexpr is one of the decl-specifiers of the decl-specifier-seq of the for-range-declaration. The identifier i is considered to be a prvalue of type std​::​ptrdiff_t; the program is ill-formed if i is not representable as such a value.

• (5.3) Otherwise, S is a destructuring expansion statement and, if N is 0, S is equivalent to:

  {
    init-statement
    constexpropt CONST-SPECIFIER auto&& range = expansion-initializer;
  }

  otherwise, S is equivalent to:

  {
    init-statement
    constexpropt CONST-SPECIFIER auto&& [u0, u1, ..., u$N$-1] = expansion-initializer ;
    S0
    ...
    SN-1
  }

  where N is the structured binding size of the type of the expansion-initializer and Si is

  {
    for-range-declaration = vi ;
    compound-statement
  }

  If the expansion-initializer is an lvalue, then vi is ui; otherwise, vi is static_cast<decltype(ui)&&>(ui). The keyword constexpr is present in the declaration of u0, u1, ..., u$N$-1 if and only if constexpr is one of the decl-specifiers of the decl-specifier-seq of the for-range-declaration.

7 A simple-declaration or a condition with a structured-binding-declaration is called a structured binding declaration ([dcl.struct.bind]). Each decl-specifier in the decl-specifier-seq shall be consteval, constexpr, constinit, static, thread_local, auto ([dcl.spec.auto]), or a cv-qualifier. The declaration shall contain at most one sb-identifier whose identifier is preceded by an ellipsis. If the declaration contains any such sb-identifier, it shall declare a templated entity ([temp.pre]).

2 Except for objects declared with the constexpr or consteval specifier, for which see [dcl.constexpr], […]

1 […] Let cv denote the cv-qualifiers in the decl-specifier-seq and S consist of each decl-specifier of the decl-specifier-seq that is constexpr, consteval, constinit, or a storage-class-specifier. […]