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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.
class virtualFieldAccess : public access {
access *getter;
access *setter;
// As an optimization, one could add a 'caller' field, to handle calls to
// functions such as 'a.push(x)' where a is an array more efficiently.
public:
virtualFieldAccess(access *getter, access *setter = 0)
: getter(getter), setter(setter) {}
virtualFieldAccess(vm::bltin getter, vm::bltin setter = 0)
: getter(new bltinAccess(getter)),
setter(setter ? new bltinAccess(setter) : 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
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