Embrace Whitespace

Icy lets you skip closing braces and semicolons by applying indentation based deduction rules. Therefore letting you write:

void BFCAllocator::SetSafeFrontier(uint64 count) {
  uint64 current = safe_frontier_.load(std::memory_order_relaxed)
  while (count > current) {
    if (safe_frontier_.compare_exchange_strong(current, count)) {
      retry_helper_.NotifyDealloc()
      return
    else {
      current = safe_frontier_.load(std::memory_order_relaxed)

instead of:

void BFCAllocator::SetSafeFrontier(uint64 count) {
  uint64 current = safe_frontier_.load(std::memory_order_relaxed);
  while (count > current) {
    if (safe_frontier_.compare_exchange_strong(current, count)) {
      retry_helper_.NotifyDealloc();
      return;
    } else {
      current = safe_frontier_.load(std::memory_order_relaxed);
    }
  }
}

Brace the rules

1. Strings, comments, trailing whitespace and empty lines are ignored.
2. If next line has higher indentation, both lines are treated as same logical line.

   • ScopeExitGuard(const bool callOnScopeExit_,
                    F &&onScopeExit_,
                    m_callOnScopeExit(callOnScopeExit_),
                    m_onScopeExit(std::forward<F>(onScopeExit_))
3. If a line ends with an opening brace and next line has exactly one level higher indentation, it marks the start of a block.

   • namespace guard { // Not a block. Must close manually
     if (m_callOnScopeExit) { // Block
         m_onScopeExit()
     std::cout << "Enter"     // Block closed
4. The line after the next logical line having indentation equal or lower than the block's start, marks the end of the block.

   • ScopeExitGuard(ScopeExitGuard<G> &&other)
         : m_callOnScopeExit(true) { // Block start at logical line's indent 0
       other.m_callOnScopeExit = false
     
     ~ScopeExitGuard() { // Previous block ends
       if (m_callOnScopeExit) {
         m_onScopeExit()
5. If a logical line has indentation equal or greater than the next line, it is treated as a statement and appended with a semi-colon.
   • The line must not end with { ; , : < ( [ =.
   • Exception for isolated template declarations.

     • template <typename G> // Not a statement
       ScopeExitGuard(ScopeExitGuard<G> &&other)
           : m_callOnScopeExit(true) {
         other.m_callOnScopeExit = false // Statement
         std::cout << "Exit" // Statement
       auto flags = {1, 2, 3}

Extras

• Icy can seamlessly integrated with existing C++ tooling since the brace and semi-colon addition is done only on the line ends which preserves line and column numbers. TODO: Extensions for popular editors. Should be trivial.
• Decompilation with icyd involves clang-format with following configuration.

  LambdaBodyIndentation: Signature
  IndentGotoLabels: true
  IndentExternBlock: Indent
  BreakBeforeBraces: Attach
  AllowAllArgumentsOnNextLine: false
  Cpp11BracedListStyle: false
  IndentRequires: true
  IndentWrappedFunctionNames: true
  NamespaceIndentation: All
  UseTab: Never
  CompactNamespaces: false
  
  Closing braces and semi-colons are removed if Icy compiler icyc can deduce them from the indentation of formatted code.

Related works

There have been a few attempts at trimming the C++ syntax but have ended up being too disruptive.

• coffeepp
• CPY
• SugerCPP