Hyrum Wright

C++ is a dynamically typed language

example with sso_string and union

If somebody can (ab)use your API, they will

Types Encode constraints

int timeout;
int number_of_pumpkins = 6*timeout;

better:

void set_deadline (absl::Duration deadline);


See “Time Programming Funamentals” by Greg Miller

Abseil Time API

• Valid invalid operations: Duration + Duration gives Duration;
Duration + Time gives Time;
Time + Time is invalid, etc

Gradual Typing

• python: adds annotation

Goals

• Automated (almost) everything
• Keep code buildable (each multiple steps)
• Keep code readable
• Eventually converge at a fixed point

Things that don’t work

• Monolithic changes
• Variable type
• Most integers don’t represent time
• Variable name
• What does timeout_seconds actually mean?
• Comments super unreliable

Types of transformations

• Expression
• Simplification
• Comparison
• Addition and Subtraction
• Distribution
• Variable
• Local, global, class members
• Inter-function
• Parame and value

Expression: Simplification

• Makes matching easier
• clang-tidy code for matcher
• code for fixer

Expresion: Comparison

Inter-function return values

Seeding Type Information

• Identify high value targets

Reactions

• You added a bug … oh
• Thanks
• (crickets)

Other applications

• Converting to std::string_view
• Ownership deduction (i.e. std::unique_ptr)

GitHub.com/llvm-mirror/clang-tools-extra/tree/master/clang-tidy/abseil

Questions

• How to justify? “We should be able to change our software”