Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Tue, 27 Sep 2005 12:56:37 -0500

Kay-Uwe Kasemir wrote:

In a few more years there will be another language.
Today, however, I have to acknowledge that C++ is the only
practical language for implementing V4.
But the APIs for strings, data access, ... could still
be kept basic enough that SWIG can translate the C++
header files into perl bindings,
a perl script could turn the C++ into objective C,
and the C++ and Java implementations also match.

Meaning:
Use 'assign' instead of 'operator =',
'isEqual' instead of 'operator ==',
'getElement' instead of 'operator []', ...

Shouldn't this also apply to dataAccess? {Or should I say :-) }

I would also like to quote the first sentence of the second paragrah of

Stroustrup "The C++ Programming Language" in the chapter titled "Strings"

"Experience shows that it is impossible to design the perfect string"

Working on the V4 database design has made me think about what it needs

for strings.

For most strings all it needs is a nonmutable string.
For these it wants to be able to pass a reference to it to arbitrary code.

It needs this for things like record type names, field names, record

instance names, menu choice names, etc. etc. Some of these may change

but very infrequently.

The string always contains UTF-8 encoded strings, which I believe can

be printed with a "%s" format if

the string is made available as a "const char *"

Perhaps the only type of string connected with an IOC record that

changes frequently is a field in a record type like stringin and

stringout. In this case the record support can do what ever it wants to

handle the string. It can even just use C style strings!!!

Thus all the IOC database needs is a:

1) nonmutable reference counted continguous string. When the reference

count goes to 0 the storage can be reclaimed

2) The ability to copy the value from a nonmutable string to a mutable

string.

In Java String and StringBuffer are all that is needed.

In C++ all that is needed is

1) A class that holds UFT-8 encoded non-mutable strings and make the

contents available as a "const char *" and it's length. The class keeps

a reference count and frees the storage when done.

2) The ability to copy the nonmutable string to a "char *" array

allocated by the requester.

That is all.

What the IOC database needs for strings is very different than what

dataAccess requires.

Marty

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System