Herb Sutter

• add things (more); fix things (some); simplify (least);
• Why not reverse this?
• adding things (eg MetaClasses) can simplify things

A tale of two compiler switches

-fno-exceptions

-fno-rtti

• Make things static by default
• Dynamic by opt-in

Exception Handling

• isocpp.org 2018-02 survey; 48% ban exceptions either fully or partially (22% not allowed)
• error codes; expected/outcome types; exceptions
• std::error_code. std::filesystem supports both dialect

Root cause

• Today’s exception handling is not zero-overhead. Just enabling increases size
• throwing an exception not statically boundable space and time overhead. Violates you can’t reasonably write it better by hand
• Lack of control

Key definition

• what is a recoverable error
• A function cannot do what it is supposed to do. Mirriam webster definition of “error”
• A precondition violation is always a bug in the caller

Four coordinated proposals

• Enable zero-overhead exception handling
• throw few exceptions (90% of all exceptions should not be)
• support explicit try for visble propagation

static exceptions

• throwing values of static types means by value. No dynamic memory
• isomorphic to error codes
• share return channel
• Need to be backward compatible. Opt in
• As-if returning union(Success; Error;} + bool
• doubles down on value semantics

Proposal

• Add a noexcept-querable allocator proprety for “reports vs aborts” on allocation failure.
• recommend conditional noexcept based on the relvant allocator
• babb on GitHub.com/HerbSutter

Part 2: Run-time type information

• Same for exceptions
• Joe Bialek Wendesday Root cause of CVEs by patch year.
• Type confusion increasing (e.g. static downcast)
• static_cast perhaps because RTTI is banned
• RTTI allowed in 68%

static_cast down-casts

• Peter Collingbourne
• Uses vtable ordered in memory so downcast is just a range check

• down_cast

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