On Wed, 3 Aug 2011, Max Vlasov wrote:
On Wed, Aug 3, 2011 at 3:34 PM, Michael Van Canneyt <[email protected]>
wrote:
On Wed, 3 Aug 2011, Alexander Klenin wrote:
I also use 'with' extensively, despite the risks,
since with the right usage the readablity gains are considerable.
2011/8/3 Max Vlasov <[email protected]>:
1. Introducing a check in the compiler setting (or a
conditional define)
that could force the developer to use self inside 'with'
constructions.
...
2. Some switch (maybe on by default) that prevents from
compiling if there
are several duplicate names in the same 'with' context
(including global,
local, fields).
Error is IMHO too severe. I think a warning if the name inside of
'with' overrides a name from outer scope
would be an acceptable compromise.
Of course, a disambiguation facility would be even better,
but I am afraid FPC developers will resist this improvement :(
Frankly, I don't understand the discussion.
I use 'with' all the time because it increases readability and reduces typing.
I don't want to be punished with heaps of warnings simply because I use a
language feature. Yes, I am aware that there are risks involved.
If you don't like 'with', then don't use it, end of story.
Introducing the proposed switch is nonsense, since it is useful only when
dealing with other people's code. For your own code, you don't need this
switch. Simply don't use 'with', and you're safe. If you type 'with' anyway,
that would be very inconsequent of you.
Michael, one example from Sql
if you write something like
SELECT * FROM Detail LEFT JOIN Master on Detail.masterid=master.id where id=34
sqlite and mysql, probably other dbms will stop you with 'ambiguous column
name' error,
Huh ? Firebird does not, and they should not.
It's clear from the statement that id is part of table 'master'.
If both tables contain a field 'id', only then they must give an error.
I assume you meant to write:
SELECT * FROM Detail LEFT JOIN Master on Detail.id=master.id where id=34
In which case the error is real.
But the analogy is flawed. In pascal, there is a clearly defined scope.
Inside a WITH, the compiler will first search the scope attached to the
identifier in with.
SQL has no scope.
The developers of these dbms could end up with some default way of context
resolving (for example the last mentioned table in the sentence), but they did
not. So many developers feel safer about the fact that if their detail table
will get some field with the same name as one of master's, the dbms won't
silently choose some field. I suppose this requirement could be even the part
of SQL-92. Talking about standards, I also admit that Wirth probably never
mentioned anything about the disambiguation resolving. But we also can be sure
that there was no objects and classes when he worked with pascal so there
were not much of a hidden context in the pascal sources.
By the way, there's the objfpc mode and it doesn't allow parameters have the
same names as field names. This is different to Delphi and generally speaking I
think this requirement lays in the same area as 'with' disambiguation if
implemented. Both serve more or less the same goal, don't they?
They do, I agree on that.
Like I said, there is a 'risk' when using with, I know this.
But I think it is very small indeed.
(in fact, last week I had such an error after refactoring code,
but it was the first time in maybe 10 years)
I just don't think that the solutions presented will make it any better.
Say you introduce a switch that forces you to use 'With'.
Then what ?
You'll have to check all 'with' statements because suddenly they no longer
compile.
I doubt this will make you find the bug.
In the worst case, you'll end up prefixing the wrong properties with 'self'.
Michael.
--
_______________________________________________
Lazarus mailing list
[email protected]
http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
