As we said above, immediate values are not pointers:
Fixnum,
Symbol,
true,
false, and
nil are stored directly in
VALUE.
Fixnum values are stored as 31-bit numbers
[Or 63-bit on
wider CPU architectures.] that are formed by shifting the original
number left 1 bit and then setting the least significant bit (bit
0) to ``1.'' When
VALUE is used as a pointer to a specific Ruby
structure, it is guaranteed always to have an LSB of zero; the
other immediate values also have LSBs of zero. Thus, a simple
bit test can tell you whether or not you have a
Fixnum.
There are several useful conversion macros for numbers as well as
other standard datatypes shown in Table 17.1 on page 174.
The other immediate values (
true,
false, and
nil) are
represented in C as the constants
Qtrue,
Qfalse, and
Qnil, respectively. You can test
VALUE variables against
these constants directly, or use the conversion macros (which perform
the proper casting).
