"Dmitry Stogov" wrote in message
news:CA+9eiLu634OpuXVT8NnwZwitqc=s4g8ubbmj+cob4nmqcpx...@mail.gmail.com...
On Thu, Feb 19, 2015 at 12:03 PM, Tony Marston <tonymars...@hotmail.com>
wrote:
"Rowan Collins" wrote in message news:54e4fac2.7060...@gmail.com...
Tony Marston wrote on 18/02/2015 10:52:
"Rowan Collins" wrote in message news:54e32caa.5030...@gmail.com...
Tony Marston wrote on 17/02/2015 09:59:
"Rowan Collins" wrote in message news:54e1c993.1070...@gmail.com...
Tony Marston wrote on 16/02/2015 10:09:
This RFC only mentions errors with object methods, so what impact
would it have with procedural functions. For example, if
fopen('nonexistantfile.txt') fails the return value is FALSE and an
E_WARNING is generated, but it is difficult to trap the error
message (it
could be a permissions error, for example). Is there any plan to
convert
procedural functions to throw exceptions?
As Nikita already said:
This RFC is strictly about fatal and recoverable fatal errors.
Changing any
other error types to exceptions would be a significant
backwards-compatibility break.
That is why I suggested that those functions could be made to switch between
throwing an exception or not based on them being included within a try ...
catch block (or not)
So, no, since that's currently an E_WARNING, there is no current
plan
to change that case to an exception. If we were writing fopen() from
scratch now, it might be worth considering, but the BC implications
of
changing something from non-fatal to fatal are rather drastic.
Currently the only values returned by fopen(), fwrite() and fclose()
indicate either success or failure, but not the reason for any failure.
That has absolutely nothing to do with OO vs procedural code,
though.
I disagree. Exceptions were originally invented to solve the semipredicate
problem which only exists with procedural functions, not object methods.
Many OO purists would like exceptions to be thrown everywhere, but this
would present a huge BC break. If it were possible get these functions to
throw an exception ONLY when they are included in a try ... catch block then
this would not break BC at all.
--
Tony Marston
A procedural function could well have an error condition which
should be
fatal if unhandled, but can usefully be caught somewhere up the
stack,
which is basically what an exception is for. Any procedural function
which
currently issues an E_ERROR or E_RECOVERABLE_ERROR is a candidate to
be
converted under the current RFC.
Regards,
The reason that I mentioned this problem with fopen() - the
difficulty
with capturing the error message if it fails - is that it also exists
with
some other functions as well, so it would be nice to be able to put
the
function in a try ..... catch block so that any and every message
could be
made available. It is quite obvious that changing fopen() to use
exceptions
would be a major BC break for all exiting applications, so my
question is
this:
Would it be possible to tell the function if it were being called in
a
try ... catch bloc or not? If it were then throw an exception, if not
then
don't throw an exception. I realise that this might be tricky to
implement,
but if it could be it would allow the developer to choose whether
he/she
wanted to use exceptions or not instead of having the choice forced
upon
him/her.
Is this possible? Or am I just dreaming?
The point of exceptions is that they don't have to be caught in the
current scope. So is the below fopen() call "in a try ... catch block"
for
the purposes of that check, or not? If putting try { ... } around an
entire
application caused all calls to fopen(), in every library it used, to
stop
returning false, you'd have exactly the same BC issue as just changing
it
permanently.
function foo() {
try
{
$data = load_data();
}
catch ( ... ) { ... }
}
function load_data() {
$fh = fopen(...);
...
}
So no, I'm afraid it's probably not possible.
Could it be restricted to the current scope? In your example the call
to
fopen() exists in the load_data() function and is not in a try ...
catch
block within *that* function, so the fact that the call to load_data()
is
within a try ... catch block should be irrelevant as it is in a
different
scope.
If the exception is only thrown when the try - catch is in the same
scope, is there really much advantage to it being an exception? When
you're
that close to the code, sticking an if ( $fh === false ) { ... } around
it
really isn't that much different from catch(IOException $e) {
The advantage is that you can obtain the reason for the error. All that
happens with fopen() at the moment is that it returns FALSE which tells
you
that it has failed, but it does not tell you why. This is a classic
example
of the semipredicate problem for which exceptions were originally
designed.
The main advantage is the ability to catch FATAL errors that previously
leaded to script termination and 500 response.
Thanks. Dmitry.
Having the problem be detectable in a higher scope is kind of the point
of exceptions.
So is the ability of catching an exception immediately it is thrown so
that you can obtain the error message. Having the ability to deal with an
exception at a higher level is only relevant if you don't deal with it
immediately, either by design or by accident.
--
Tony Marston
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