1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
/*****
* 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
|
