# Changeset 41fcd94 for doc/papers

Ignore:
Timestamp:
Feb 8, 2018, 4:52:56 PM (4 years ago)
Branches:
aaron-thesis, arm-eh, cleanup-dtors, deferred_resn, demangler, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, resolv-new, with_gc
Children:
ff878b7
Parents:
06b176d (diff), eb7f20c (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.
Message:

Merge branch 'master' of plg2:software/cfa/cfa-cc

File:
1 edited

### Legend:

Unmodified
 r06b176d In \CFA, the address of a @T&@ is a lvalue @T*@, as the address of the underlying @T@ is stored in the reference, and can thus be mutated there. The result of this rule is that any reference can be rebound using the existing pointer assignment semantics by assigning a compatible pointer into the address of the reference, \eg @&r1 = &x;@ above. This rebinding can occur to an arbitrary depth of reference nesting; $n$ address-of operators applied to a reference nested $m$ times will produce an lvalue pointer nested $n$ times if $n \le m$ (note that $n = m+1$ is simply the usual C rvalue address-of operator applied to the $n = m$ case). The explicit address-of operators can be thought of as cancelling out'' the implicit dereference operators, \eg @(&*)r1 = &x@ or @(&(&*)*)r3 = &(&*)r1@ or even @(&*)r2 = (&*)*r3@ for @&r2 = &r3@. This rebinding can occur to an arbitrary depth of reference nesting; loosely speaking, nested address-of operators will produce an lvalue nested pointer up to as deep as the reference they're applied to. These explicit address-of operators can be thought of as cancelling out'' the implicit dereference operators, \eg @(&*)r1 = &x@ or @(&(&*)*)r3 = &(&*)r1@ or even @(&*)r2 = (&*)*r3@ for @&r2 = &r3@. More precisely: \begin{itemize} \item if @R@ is an rvalue of type {@T &@$_1 \cdots$@ &@$_r$} where $r \ge 1$ references (@&@ symbols) than @&R@ has type {@T *&@$_{\color{red}2} \cdots$@ &@$_{\color{red}r}$}, \\ \ie @T@ pointer with $r-1$ references (@&@ symbols). \item if @L@ is an lvalue of type {@T &@$_1 \cdots$@ &@$_l$} where $l \ge 0$ references (@&@ symbols) then @&L@ has type {@T *&@$_{\color{red}1} \cdots$@ &@$_{\color{red}l}$}, \\ \ie @T@ pointer with $l$ references (@&@ symbols). \end{itemize} Since pointers and references share the same internal representation, code using either is equally performant; in fact the \CFA compiler converts references to pointers internally, and the choice between them in user code can be made based solely on convenience. In particular, \CFA does not implement class-based encapsulation: neither the constructor nor any other function has privileged access to the implementation details of a type, except through the translation-unit-scope method of opaque structs provided by C. In \CFA, a constructor is a function named @?{}@, while a destructor is a function named @^?{}@; like other \CFA operators, these names represent the syntax used to call the constructor or destructor, \eg @S s = { ... };@ or @^(s){};@. In \CFA, a constructor is a function named @?{}@, while a destructor is a function named @^?{}@; like other \CFA operators, these names represent the syntax used to call the constructor or destructor, \eg @x{ ... };@ or @^x{};@. Every constructor and destructor must have a return type of @void@, and its first parameter must have a reference type whose base type is the type of the object the function constructs or destructs. This first parameter is informally called the @this@ parameter, as in many object-oriented languages, though a programmer may give it an arbitrary name. \begin{cfa} Array a, b; (a){};                                  $\C{// default construct}$ (b){ a };                               $\C{// copy construct}$ ^(a){};                                 $\C{// destruct}$ (a){ 5, 0xFFFFFFFF };   $\C{// explicit constructor call}$ a{};                            $\C{// default construct}$ b{ a };                         $\C{// copy construct}$ ^a{};                           $\C{// destruct}$ a{ 5, 0xFFFFFFFF };     $\C{// explicit constructor call}$ \end{cfa}