Re: [HACKERS] proposal: session server side variables - Mailing list pgsql-hackers

From Fabien COELHO
Subject Re: [HACKERS] proposal: session server side variables
Date
Msg-id alpine.DEB.2.20.1612290914360.4911@lancre
Whole thread Raw
In response to Re: [HACKERS] proposal: session server side variables  (Pavel Stehule <pavel.stehule@gmail.com>)
Responses Re: [HACKERS] proposal: session server side variables
List pgsql-hackers
Hello Pavel,

>> Hmmm... I know a little bit about that field, ISTM that you are speaking
>> of the current capabilities of a particular static analysis tool, but I'm
>> not sure that the tool capabilities could not be enhanced to manage more
>> things.
>
> It cannot be - the static analyze is limited to function scope - in static
> analyze you don't know a order of calls.

I have been doing interprocedural static analysis for the last 25 years, 
and I can assure you that those techniques are not limited to the scope of 
a function. As for global variables, I agree that you may proove more 
things about them if you know the order of calls.

>> The private session variables I suggested have a fixed (static) name, and
>> their type could be infered by a static analysis tool, eg:
>>   ...
>>   DECLARE @foo BOOLEAN PRIVATE;
>>   -- I know that there is private a boolean variable "@foo" of unknown
>> value
>>   SET @foo = TRUE;
>>   --- I know that @foo is true...
>>   ...
>
> This is not too friendly

Friendly is subjective. ISTM That it gets the job done with minimal syntax 
and implementation. It avoids getter/setter functions which are unfriendly 
to me.

> - you have to repeat DECLARE in every function.

That is the same in nearly all programming languages, you have to declare 
external variables somehow before using them, that is life.

Some declarations could be avoided if an unknown variable is assumed to 
have untyped value NULL by default.

> What is somebody somewhere write @fooo

NULL ? Unkown variable error ?

> or use DECLARE @foo integer instead.

It would not matter if it is someone else, because @foo would be their 
private version. If it is yourself, an error could be raised if a session 
variable is found to be declared with two distinct types. A static 
analysis tool would be able to detect that as well.

> There is big space for errors.

Whatever the features and syntax, you can always shoot yourself in the 
foot.

I have open a wiki page to help with this discussion:
    https://wiki.postgresql.org/wiki/Variable_Design

-- 
Fabien.



pgsql-hackers by date:

Previous
From: Fabien COELHO
Date:
Subject: Re: [HACKERS] proposal: session server side variables
Next
From: Pavel Stehule
Date:
Subject: Re: [HACKERS] proposal: session server side variables