Is there a *direct* way to overwrite a symbol definition?

a equ 123
a equ 456
a equ 789    

gandalf wrote:

Is there a *direct* way to overwrite a symbol definition?

You can always overload

Code:

a equ 123
a equ 456
a equ 789    

But the original value of 'a' is now buried 4 deep in the equ 'stack'.

The define directive followed by the name of constant and then the value, is the alternative way of defining symbolic constant. The only difference between define and equ is that define assigns the value as it is, it does not replace the symbolic constants with their values inside it.

a equ a b

became

tmp equ a b
restore a
a equ tmp
restore tmp    

The "define" wouldn't help him with this sample, I think. What he's trying to do is to make "a" have no stacked definitions, so he need to restore value of "a" before defining it with new value - and since the new value refers to "a" already, he needs temporary variable.

But, by the way: there is no point in doing "restore" unless you really need to get back the previous value - with fasm's preprocessor architecture you don't even gain any memory back by doing "restore".

You'd hardly get any noticeable performance improvement by making them discard the previous values. It's the growing preprocessed source that eats your memory when you have thousands of those definitions (and this source is generated and kept anyway), the lookup tables contain just merely pointer to the content in the source. Preprocessor was designed with the restorable content in mind (exactly same goes with "purge"), so to gain anything from such idea you'd perhaps have to write another preprocessor.

But wouldn't it hurt performance a little too much?

I use a few global definitions that are updated many times. Restoring them after many updates is not easy and what would happen if someone else were using them (i.e. symbols with the same names)?

The same problem applies to all the macros that use some global variables - I usually use the name@package name form, which is very unlikely to be used elsewhere.

As for restoring the definitions that are updated frequently: what do you need to restore them for? If you really need the original value, then store it in some other variable at startup.

gandalf wrote:

But wouldn't it hurt performance a little too much?

Is performance really the issue here? How much time is saved/lost?

That's not a very safe solution (it reminds me of TeX and all its problems when it grew up).

That's exactly what I did before. But now my code is much cleaner.
Every macro overwrites/returns "output" variables and any other modifications are transient. That way, if the user wants to preserve a definition, say curExpr, they just write:
curExpr equ ; dummy value
matchExpr ; overwrites curExpr
restore curExpr

gandalf wrote:

That's not a very safe solution (it reminds me of TeX and all its problems when it grew up).

Well, you have to reserve some names anyway - even the names of your macro get reserved this way (what if someone already had a macro called the same as one of your macros?). I don't see anything unusal here.

So it would be enough to use some other variable internally, and assign value to "curExpr" just once in your macro - so that you have separate internal "working" variable (which you can even define as local to macro, and this way ensure no name conflicts will arise at all), and separate official external interface variable for output.

If I invoke the same macro 1000 times does the final code contain 1000 expansions of that macro???