On 22/10/11 10:01, Mark Morgan Lloyd wrote:
Felipe Monteiro de Carvalho wrote:
Free is how you release the memory allocated for a object. Free calls
Destroy. Never call Destroy manually. When you implement the
destructor you always implement Destroy, never change Free.
A number of years ago, Matthew Jones's wife looked over his shoulder
and caught him using Create and Destroy. "Bit violent, isn't it?" When
he told the story somebody else pointed out that he should be using
Create and Free, I find this anecdote makes it easy to remember.
Nil is not a routine, it is a value, it means that the object is
empty, it does not exist / is not allocated. Nil in existing
implementations that I know is represented by the value zero.
I've once seen a compiler using a non-zero value, I think it was the
first Logitech protected-mode Modula-2 and it used ffff:0000. Apart
from that I think that C specifies that nil has a bit pattern of all
zeros, and anything with even the slightest interest in compatibility
sticks to this as a convention.
Almost -- In C, NULL doesn't have to be all zeroes internally, but the
value 0 in the source code represents the NULL pointer. The compiler is
allowed to convert (void*)0 to a different bit pattern if the hardware
requires it, but you'd need a pretty good reason to make life that
complicated. So it would be a rare compiler that did that.
If I recall corerctly, that Modula-2 value for nil was the address the
8086 jumped to when released from RESET. So jumping through a pointer
with value nil would be something you would notice pretty much immediately.
FP
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