Annex G (informative) Ill-formed, no diagnostic required [ifndr]

G.6 [dcl]: Declarations [ifndr.dcl]

G.6.5[ifndr:dcl.fct.def.replace.bad.replacement]
Specified in: [dcl.fct.def.replace]

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A declaration of a replaceable function that is inline, not attached to the global module, does not have C++ language linkage, does not have the required return type, or is not a valid redeclaration of the corresponding declaration in a standard library header (if there is one) then the program is ill-formed, no diagnostic required.
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[Example 1: extern "C" // IFNDR, wrong language linkage inline // IFNDR, inline int // IFNDR, wrong return type handle_contract_violation(const std::contracts::contract_violation&) {} void* operator new(decltype(sizeof(0))) noexcept; // IFNDR, mismatched exception specification to // declaration in <new> — end example]