SCPP26 Language Standard

Status: Working draft. Incomplete – clauses are added incrementally; absence of a clause on some topic means this document does not yet modify the C++ standard’s treatment of that topic, not that SCPP26 has no rule for it (see the book for the topics not yet formalized here).

1 Scope

1. This document specifies the form and establishes the interpretation of programs written in the SCPP26 programming language.

2. SCPP26 is defined as ISO/IEC 14882:2026, Programming languages — C++ (hereafter “the C++ standard” or “C++26”), modified as specified by the following clauses. Except as explicitly modified by a later clause of this document, every requirement of the C++ standard applies to a SCPP26 program unchanged.

3. This document identifies SCPP26’s departure from the C++ standard by difference only: the small number of new syntactic forms it introduces (see Clause 5 for the first), the additional semantic restrictions and static checks it imposes on programs the C++ standard would otherwise accept without further constraint, and, where a later clause states so explicitly, constructs the C++ standard permits that this document does not.

4. Conformance to this document requires conformance to the C++ standard as modified herein; this document does not by itself define a complete programming language.

2 Normative references

1. The following referenced document is indispensable for the application of this document: ISO/IEC 14882:2026, Programming languages — C++.

2. For undated references, the latest edition of the referenced document (including any amendments) applies.

3 Terms and definitions

For the purposes of this document, the terms and definitions given in the C++ standard apply, together with the following.

3.1 erasure the source-level transformation of a SCPP26 translation unit obtained by removing every attribute whose attribute-namespace ([dcl.attr.grammar]) is scpp.

[Note: Clause 4 requires the result to be a well-formed C++26 translation unit. Because every SCPP26-specific construct is spelled as an attribute in the scpp attribute-namespace – including [[scpp::unsafe]] (§5) – this is the transformation’s only step; this document introduces no keyword, operator, or other token a real C++26 compiler cannot already parse and silently ignore unmodified (see also Clause 4 (2)’s note on -Wno-unknown-attributes). — end note]

3.2 safe context any point in a SCPP26 program that is not part of an unsafe context (3.3).

3.3 unsafe context either of the following: (3.3.1) a compound-statement to which an attribute-specifier-seq containing the attribute-token unsafe in the scpp attribute-namespace appertains (§5), together with every point lexically enclosed by it; or (3.3.2) the entire function-body ([dcl.fct.def.general]) of a function to which an attribute-specifier-seq containing the attribute-token unsafe in the scpp attribute-namespace appertains (§5), together with every point lexically enclosed by it.

3.4 gated operation an operation this document identifies as ill-formed in a safe context (3.2) and well-formed in an unsafe context (3.3).

4 Conformance

1. A conforming implementation shall issue at least one diagnostic message for every SCPP26 translation unit that is ill-formed under this document or under the C++ standard as modified by this document, except where this document explicitly permits an implementation to forgo diagnosing a specific ill-formed construct.

2. A conforming implementation shall accept the erasure (3.1) of every well-formed SCPP26 translation unit as a well-formed C++26 translation unit.

[Note: because erasure (3.1) only ever removes scpp-namespaced attributes, and a C++26 compiler already accepts an unrecognized attribute unmodified ([dcl.attr.grammar]), a well-formed SCPP26 translation unit is itself already accepted by a conforming C++26 implementation even before erasure – typically subject only to an unknown-attribute diagnostic, which an implementation’s own options (for example, a command-line option resembling -Wno-unknown-attributes) may be used to suppress. Erasure (3.1) remains the only transformation this document requires a conforming implementation to accept; it exists to produce output free of any such diagnostic, not to make the translation unit compilable in the first place. — end note]

[Note: this document may require an implementation to perform an additional runtime check (for example, a future clause’s arithmetic-overflow check) that C++26 does not require when translating the same erased text; the observable behavior of the two need therefore not coincide for an execution that would trigger such a check. — end note]

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