Re: Bug in 1.5a ?
Apparently a lot of people have been severely confused
by the "global" keyword in Euphoria. I will improve
the description in REFMAN.DOC. See also
TROUBLE.DOC if you have found that
routines / vars declared in an include file are
reported as "not declared" when you try to
use them in another file.
The situation is this:
If you declare a constant, variable or routine and you do not
put the keyword "global" in front of the declaration,
that variable or routine declaration will become
invisible at the end of its file. It will not be accessible
from any other file. e.g.
-- file x.e
global procedure foo()
end procedure
Without the word "global", foo() would be unknown outside
of x.e. It would only be known inside x.e from the point where
it is declared to the end of x.e. Only code in x.e after the
declaration of foo() would be able to call foo().
With the word "global", foo() will be visible from the point it
is declared right through the rest of the program, in all other
files.
Many people wrongly assume that "global" is the default,
and are puzzled when a declared routine or variable
is said to be "not declared" when called from another
file. I guess that's because BASIC doesn't have this concept,
and in C it's inverted - global is the default situation and
you need the optional keyword "static" to *prevent* a routine or variable
from being known outside of its file. The guy who invented C++
(Stroustrup) has stated that C has it wrong - it should have
been defined the other way (Euphoria's way), i.e. default to
"not global".
Why bother with all this?
Consider that you make a .e include file for other people to use.
Suppose your include file has 20 routines and 30 variables,
but the user of your file should only use 2 of the routines and
none of the variables. Without the global/not-global feature,
you would have to add 20+30 = 50 names to his program,
names that he is not allowed to use. This might cause naming
conflicts for him and he would
have to change some of his names or some of your names.
Furthermore, the global keyword would help to remind him of which
routines/variables he can legitimately use, and which are
internal to your code.
When you later modify your .e file, it will help you to know
that some routine or variable is
not global, therefore you will not break other people's code by
changing/removing it.
If global were the default, people would be lazy and there
would be many internal routines/vars exposed as global
that needn't be. With "not global" as the default, the tendency is
that only the routines/vars that actually need to be global will
be declared that way.
Regards,
Rob Craig
Rapid Deployment Software
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