Declarative Control Flow

Abstract

Getting exception handling right is a perennial problem in C++ that has eluded systematization. Not for much longer. New language and library developments make it possible to handle exceptions in a declarative manner, leading to drastic code simplification.

This talk discusses an alternative approach to handling exceptional flow that eliminates the need for small ancillary RAII classes, try/catch statements that rethrow, and other cleanup mechanisms. The popular Scope Guard idiom gets a spectacular generalization. Statements specify in a declarative manner actions to be taken if the current scope is left normally or via an exception. The resulting code is simpler, smaller, and easier to maintain.

Highlights

• Review ScopeGuard's pros and cons
• Stay abreast of proposed language improvements for better error handling
• New implementation-specific extensions to scope guards
• Use of the new SCOPE_FAILURE and SCOPE_SUCCESS abstractions that complements the existing SCOPE_EXIT

Attendee Profile

ScopeGuard is of interest to C++ programmers of all levels. Implementation details are appealing to advanced engineers.

Outline

• Motivation
  • Action/Next/Cleanup/Rollback idiom overview in several languages
  • Composition with said idiom
  • Explicit vs. implicit control flow as a riff on declarative vs. imperative programming
• Implementation
  • Underpinnings
  • gcc/clang
  • MSVC 8.0+
  • Layering
  • Icing
  • Cake Candles
• Use Cases
  • Tracing
  • Transactional Work
  • Order Still Matters
  • nothrow notes
  • Scope Changes
  • Legacy code