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+/*****
+ * virtualfieldaccess.h
+ * Andy Hammerlindl 2009/07/23
+ *
+ * Implements the access subclass used to read and write virtual fields.
+ *****/
+
+#include "access.h"
+
+namespace trans {
+// In code such as
+// pair z; write(z.x);
+// to evaluate the expression z.x, first z is pushed onto the stack, then as
+// it is not a record, instead of accessing its field in the usual way for a
+// record, a builtin function is called which pops z off the stack and
+// replaces it with z.x. virtualFieldAccess provides the access for the
+// virtualField 'x', and 'getter' is the access to the builtin function which
+// replaces z with z.x.
+//
+// If the virtual field z.x were mutable, then setter would access a builtin
+// function, which pops a real number and then z off of the stack, sets the
+// z.x to that new value, and puts the value back on the stack. In this case,
+// pairs are immutable, but other virtual fields may not be.
+//
+// Some virtual fields are functions, such as a.push for an array a. In rare
+// cases, code such as
+// void f(int) = a.push;
+// requires an object representing a.push, and so a getter for the field must
+// be provided. Most of the time, however, these fields are just called.
+// As an optimization, a caller access can be provided. If this access is
+// given, then a call to the virtualFieldAccess just translates into a call to
+// caller.
+class virtualFieldAccess : public access {
+ access *getter;
+ access *setter;
+ access *caller;
+
+public:
+ virtualFieldAccess(access *getter,
+ access *setter = 0,
+ access *caller = 0)
+ : getter(getter), setter(setter) {}
+
+ virtualFieldAccess(vm::bltin getter,
+ vm::bltin setter = 0,
+ vm::bltin caller = 0)
+ : getter(new bltinAccess(getter)),
+ setter(setter ? new bltinAccess(setter) : 0),
+ caller(caller ? new bltinAccess(caller) : 0) {}
+
+ void encode(action act, position pos, coder &e);
+ void encode(action act, position pos, coder &e, frame *);
+
+ // Attempting to WRITE a read-only field will give an error, but if the
+ // error is caught at a higher level, a better error message (including the
+ // name of the field) can be given. This function allows such handling.
+ bool readonly() {
+ return (bool)setter;
+ }
+};
+
+} // namespace trans