Re: How to avoid throwing an exceptions for a built-in function?
On Saturday, 13 May 2017 at 09:51:40 UTC, k-five wrote: On Saturday, 13 May 2017 at 09:05:17 UTC, Jonathan M Davis But obviously, to know what's actually happening with your code, you're going to have to profile and benchmark it - Can you please give a link or page or something to read about profile or benchmark. I have no experience with those. Profiling: Halfway down this page: http://www.digitalmars.com/ctg/trace.html Two programs for visualising bottlenecks: https://bitbucket.org/andrewtrotman/d-profile-viewer https://code.dlang.org/packages/profdump Benchmarking: https://youtu.be/QELK73JSpFk?list=PL3jwVPmk_PRxo23yyoc0Ip_cP3-rCm7eB (fresh from DConf) https://dlang.org/library/std/datetime/benchmark.html https://code.dlang.org/packages/std_benchmark https://code.dlang.org/packages/benchmarkplotter
Re: How to avoid throwing an exceptions for a built-in function?
On Saturday, 13 May 2017 at 09:05:17 UTC, Jonathan M Davis wrote: For the most part, when parsing a string, std.conv.to's approach of just parsing the string and throwing an exception if/when it fails is the most efficient, because it's only going to parse the string once, whereas calling a function to validate the string's format and _then_ do the conversion would mean parsing the string twice.It's just that if you are in a situation where the string is likely not to be in the correct format, then having a bunch of exceptions thrown will harm performance. To best handle that, we'd need an alternate conversion function that did something like return the failure condition and passed the result via an out parameter or one which took a default value and returned that on failure instead of what was actaully parsed. So, ideally, we'd have other functions in std.conv to handle such cases, but in the vast majority of cases, throwing an exception on failure is going to be the most efficient solution. I did not know this. But obviously, to know what's actually happening with your code, you're going to have to profile and benchmark it - Can you please give a link or page or something to read about profile or benchmark. I have no experience with those. --- For a such purpose I already used std::stringstream in C++, and I assumed may or may not D has a such family. ( to!, parse!, ... ) Not only an invalid string like "word" for to!int, makes it being thrown, but an empty string like: "" also makes it. string str = "word"; int index = to!int( str ); // throws str = ""; int index = to!int( str ); // throws, as well! Of course throwing is useful some times, but definitely not ALWAYS, and it is better to have a convert function that never throws anything. Although [Andrei Alexandrescu] told me that the parse! family is used for such a case: Use the "parse" family: https://dlang.org/phobos/std_conv.html#parse -- Andrei but it throws as well.
Re: How to avoid throwing an exceptions for a built-in function?
On Saturday, 13 May 2017 at 08:50:20 UTC, k-five wrote:
Way arguing when a simple code can clarify the subject? right?
If am not clear so consider me as an stupid man, no problem at
all.
but CAN you please solve it for me?
import std.stdio: writeln;
import std.conv:to;
void main( string[] args ){
string str = "10";
int index;
index = to!int( str ); // okay, no exception are thrown
str = "some-words";
index = to!int( str ); // problem, an exception is thrown
}
Please run this code and convert "some-words" to int by using
to! function without facing any exception. Thanks
Please don't take it the wrong way. It just seems that Mike was
as confused by your questions as I was initially. But it's clear
that's just the language barrier, nothing more. See, you said:
Why I do not want to take care of that? Because I just need the
value, if the string is valid, otherwise no matter what the
value of string is.
...but it doesn't make sense to have an int "value" for a string
like "some-words". *Unless* one defines a "not-a-number"
equivalent for an int, i.e. 0 or some other value. That part was
hard to infer from what you were saying :) It might've been
obvious for you, but hard to understand from what you wrote.
This was what made things clear:
I just want to silent this exception...
Mostly, the source of the confusion was the "I don't want to
handle the exception". But in fact what you were asking was was
there a way to somehow ignore the exception and just return some
predefined value in case of an error. So in fact, you did want to
handle the exception (or rather, an exceptional case), you just
wanted to do it without inserting control flow instructions
(try/catch) into your code. I think the latter part already got
covered in others' replies.
Nobody was trying to insult you. With this being a multi-lingual
and multi-cultural community, remember that understanding goes
both ways, and we're sometimes caught right in the middle, in the
clash of mentalities.
Re: How to avoid throwing an exceptions for a built-in function?
On Friday, May 12, 2017 10:42:18 H. S. Teoh via Digitalmars-d-learn wrote: > On Fri, May 12, 2017 at 12:47:04PM +0200, ag0aep6g via Digitalmars-d-learn wrote: > > On 05/12/2017 10:32 AM, k-five wrote: > > > Interesting! I was worried about performance and for that I did not > > > want to use try-catch. > > > So (isNumberic) is a good solution. > > > http://dlang.org/phobos/std_traits.html#isNumeric > > > > If you're doing this for speed, you better be benchmarking. Exceptions > > are slow when they're thrown. But if no exception is being thrown, > > try-catch is probably faster than checking isNumeric beforehand. > > Yes, when it comes to performance-related issues, always profile, > profile, profile. (Or benchmark, benchmark, benchmark. Anything that > gives you actual measurements rather than subjective judgment calls.) > Far too often, what we think will perform poorly is actually nowhere > near the real bottleneck in the program, and we end up wasting too much > time "optimizing" something that doesn't even make a noticeable > difference in the end. Whereas, using a profiler early on will help you > zero in on the real bottlenecks, and you could potentially make huge > performance savings with much less effort. For the most part, when parsing a string, std.conv.to's approach of just parsing the string and throwing an exception if/when it fails is the most efficient, because it's only going to parse the string once, whereas calling a function to validate the string's format and _then_ do the conversion would mean parsing the string twice. It's just that if you are in a situation where the string is likely not to be in the correct format, then having a bunch of exceptions thrown will harm performance. To best handle that, we'd need an alternate conversion function that did something like return the failure condition and passed the result via an out parameter or one which took a default value and returned that on failure instead of what was actaully parsed. So, ideally, we'd have other functions in std.conv to handle such cases, but in the vast majority of cases, throwing an exception on failure is going to be the most efficient solution. But obviously, to know what's actually happening with your code, you're going to have to profile and benchmark it - especially if you're throwing exceptions on a regular basis but not super frequently, because then it's quickly an open question as to whether parsing twice to avoid the exception or letting the exception be thrown and caught would be faster. Odds are though that unless you're converting in a tight loop, the relative costs won't matter much, even if one is clearly more expensive than the other, simply because it's not a bottleneck in your program. But you won't know that for sure unless you profile. However, unless you're parsing a lot of invalid strings, I'd be very surprised if always parsing twice were more efficient than parsing only once and throwing an exception on failure. And D exceptions are fairly efficient at this point if you don't call toString, because we stripped out most of the string processing that they were doing up front before. It used to be pretty painful when you did a lot of tests that tested the error cases, because the exceptions really increased the time that the tests took, but that's no longer the case (IIRC, the improvements literally saved seconds of execution time in std.datetime's unit tests). - Jonathan M Davis
Re: How to avoid throwing an exceptions for a built-in function?
On Saturday, 13 May 2017 at 02:40:17 UTC, Mike B Johnson wrote:
You are not making a lot of sense:
1. Exception do bubble up, so you don't need to "handle"
exceptions at the call site if you don't want to. The whole
point of exceptions is do effectively do what you want.
2. You say that you don't have to deal with it in your code but
you are trying to deal with it now.
You are not clear on exactly what you are trying to accomplish.
Can you be more specific on why you do not want to add a
try/catch/if-else/ifThrown/etc? Is it because you don't need to
handle it in your own usage? If that is true, will others ever
use it?
Basically all you have to do is ask yourself this:
"Do I need to EVER handle the case where the data is invalid?"
If you do(e.g., other users will use your code) then you better
implement some type of exception handling. Else all you have to
do is always put in the right data(not good because it might
bite you in the ass one day).
If you just want less noise when the program crashes, just put
a try/catch block in main and catch all generic exceptions and
exit with a simple error message like "There was an ERROR, I do
not know why...".
Way arguing when a simple code can clarify the subject? right?
If am not clear so consider me as an stupid man, no problem at
all.
but CAN you please solve it for me?
import std.stdio: writeln;
import std.conv:to;
void main( string[] args ){
string str = "10";
int index;
index = to!int( str ); // okay, no exception are thrown
str = "some-words";
index = to!int( str ); // problem, an exception is thrown
}
Please run this code and convert "some-words" to int by using to!
function without facing any exception. Thanks
Re: How to avoid throwing an exceptions for a built-in function?
On Thursday, 11 May 2017 at 16:07:22 UTC, k-five wrote:
On Wednesday, 10 May 2017 at 21:19:21 UTC, Stanislav Blinov
wrote:
On Wednesday, 10 May 2017 at 15:35:24 UTC, k-five wrote:
On Wednesday, 10 May 2017 at 14:27:46 UTC, Stanislav Blinov
---
I don't understand. If you don't want to take care of
exceptions, then you just don't do anything, simply call
to!int(str).
Well I did that, but when the string is a valid type like: "10"
there is no problems. But when the string is not valid, like:
"abc", then to! function throws an exception.
Why I do not want to take care of that? Because I just need the
value, if the string is valid, otherwise no matter what the
value of string is.
First I just wrote:
index = to!int( user_apply[ 4 ] );
And this code is a part of a command-line program and the user
may enter anything. So, for a valid string:
./program '10' // okey
but for:
./program 'non-numerical' // throws an exception an 10 lines of
error appear on the screen( console )
I just want to silent this exception. Of course it is useful
for handling when someone wants to. But in my code I no need to
handle it. So I want to silent that, without using
try{}catch(){} block. I just wondered about try-catch and I
want to know may there would be a better way instead of a dummy
try-catch block.
Thanks for replying and mentioning. And I am sorry, since I an
new in English Writing, if you got confuse.
You are not making a lot of sense:
1. Exception do bubble up, so you don't need to "handle"
exceptions at the call site if you don't want to. The whole point
of exceptions is do effectively do what you want.
2. You say that you don't have to deal with it in your code but
you are trying to deal with it now.
You are not clear on exactly what you are trying to accomplish.
Can you be more specific on why you do not want to add a
try/catch/if-else/ifThrown/etc? Is it because you don't need to
handle it in your own usage? If that is true, will others ever
use it?
Basically all you have to do is ask yourself this:
"Do I need to EVER handle the case where the data is invalid?"
If you do(e.g., other users will use your code) then you better
implement some type of exception handling. Else all you have to
do is always put in the right data(not good because it might bite
you in the ass one day).
If you just want less noise when the program crashes, just put a
try/catch block in main and catch all generic exceptions and exit
with a simple error message like "There was an ERROR, I do not
know why...".
Re: How to avoid throwing an exceptions for a built-in function?
On Fri, May 12, 2017 at 12:47:04PM +0200, ag0aep6g via Digitalmars-d-learn wrote: > On 05/12/2017 10:32 AM, k-five wrote: > > Interesting! I was worried about performance and for that I did not > > want to use try-catch. > > So (isNumberic) is a good solution. > > http://dlang.org/phobos/std_traits.html#isNumeric > > If you're doing this for speed, you better be benchmarking. Exceptions > are slow when they're thrown. But if no exception is being thrown, > try-catch is probably faster than checking isNumeric beforehand. Yes, when it comes to performance-related issues, always profile, profile, profile. (Or benchmark, benchmark, benchmark. Anything that gives you actual measurements rather than subjective judgment calls.) Far too often, what we think will perform poorly is actually nowhere near the real bottleneck in the program, and we end up wasting too much time "optimizing" something that doesn't even make a noticeable difference in the end. Whereas, using a profiler early on will help you zero in on the real bottlenecks, and you could potentially make huge performance savings with much less effort. T -- Beware of bugs in the above code; I have only proved it correct, not tried it. -- Donald Knuth
Re: How to avoid throwing an exceptions for a built-in function?
On 05/12/2017 10:32 AM, k-five wrote: Interesting! I was worried about performance and for that I did not want to use try-catch. So (isNumberic) is a good solution. http://dlang.org/phobos/std_traits.html#isNumeric If you're doing this for speed, you better be benchmarking. Exceptions are slow when they're thrown. But if no exception is being thrown, try-catch is probably faster than checking isNumeric beforehand.
Re: How to avoid throwing an exceptions for a built-in function?
On Friday, 12 May 2017 at 09:03:39 UTC, Jonathan M Davis wrote: That's the wrong isNumeric. Unfortunately, both std.string and std.traits have an isNumeric. std.traits.isNumeric is an eponymous template that tests whether a type is an integral or floating point type, whereas std.string.isNumeric is a templated function which tests whether a string (or other range of characters) represents an integer or floating point literal. So, std.traits.isNumeric won't work at all for what you want, and std.string.isNumeric will sort of do what you want - the main caveat being that it will also accept floating point values, whereas to!int will not. So, if you have auto i = str.isNumeric ? to!int(str).ifThrown(0) : 0; then it will work but will still throw (and then be caught by ifThrown) if str is a floating point value. Alternatively, you could check something like auto i = str.all!isDigit ? to!int(str).ifThrown(0) : 0; (where all is in std.algorithm and isDigit is in std.ascii), and that _almost_ wouldn't need ifThrown, letting you do auto i = str.all!isDigit ? to!int(str) : 0; except that str could be an integral value that wouldn't fit in an int, in which case to!int would throw. But std.string.isNumeric will work so long as you're willing to have have an exception be thrown and caught if the string is a floating point literal. - Jonathan M Davis - Thank you for mentioning it. Since I had seen D-conference 2016 in YouTube and it talked about isNumeric in std.traits, then I used std.traits. and does not worked as I wanted. But std.string: isNumeric, worked. string str = "string"; int index = str.isNumeric ? to!int( str ) : 0; writeln( "index: ", index ); // 0 and without throwing any exceptions
Re: How to avoid throwing an exceptions for a built-in function?
On Friday, May 12, 2017 08:32:03 k-five via Digitalmars-d-learn wrote: > On Thursday, 11 May 2017 at 19:59:55 UTC, Jordan Wilson wrote: > > On Thursday, 11 May 2017 at 18:07:47 UTC, H. S. Teoh wrote: > >> On Thu, May 11, 2017 at 05:55:03PM +, k-five via > >> > >> Digitalmars-d-learn wrote: > >>> On Thursday, 11 May 2017 at 17:18:37 UTC, crimaniak wrote: > >>> > On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote: > >>> - > > > > This reason is why I sometimes use isNumeric if I have heaps of > > strings I need to convert, to reduce exceptions. So something > > like: > > int index = (str.isNumeric) ? to!int(str).ifThrown(0) : 0; > > > > Jordan > > -- > Interesting! I was worried about performance and for that I did > not want to use try-catch. > So (isNumberic) is a good solution. > http://dlang.org/phobos/std_traits.html#isNumeric That's the wrong isNumeric. Unfortunately, both std.string and std.traits have an isNumeric. std.traits.isNumeric is an eponymous template that tests whether a type is an integral or floating point type, whereas std.string.isNumeric is a templated function which tests whether a string (or other range of characters) represents an integer or floating point literal. So, std.traits.isNumeric won't work at all for what you want, and std.string.isNumeric will sort of do what you want - the main caveat being that it will also accept floating point values, whereas to!int will not. So, if you have auto i = str.isNumeric ? to!int(str).ifThrown(0) : 0; then it will work but will still throw (and then be caught by ifThrown) if str is a floating point value. Alternatively, you could check something like auto i = str.all!isDigit ? to!int(str).ifThrown(0) : 0; (where all is in std.algorithm and isDigit is in std.ascii), and that _almost_ wouldn't need ifThrown, letting you do auto i = str.all!isDigit ? to!int(str) : 0; except that str could be an integral value that wouldn't fit in an int, in which case to!int would throw. But std.string.isNumeric will work so long as you're willing to have have an exception be thrown and caught if the string is a floating point literal. - Jonathan M Davis
Re: How to avoid throwing an exceptions for a built-in function?
On Friday, 12 May 2017 at 08:32:03 UTC, k-five wrote: On Thursday, 11 May 2017 at 19:59:55 UTC, Jordan Wilson wrote: On Thursday, 11 May 2017 at 18:07:47 UTC, H. S. Teoh wrote: On Thu, May 11, 2017 at 05:55:03PM +, k-five via Digitalmars-d-learn wrote: On Thursday, 11 May 2017 at 17:18:37 UTC, crimaniak wrote: > On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote: - This reason is why I sometimes use isNumeric if I have heaps of strings I need to convert, to reduce exceptions. So something like: int index = (str.isNumeric) ? to!int(str).ifThrown(0) : 0; Jordan -- Interesting! I was worried about performance and for that I did not want to use try-catch. So (isNumberic) is a good solution. http://dlang.org/phobos/std_traits.html#isNumeric NOT a GOOD solution! Since it accept type and NOT variable: so: index = (str.isNumeric) ? to!int(str).ifThrown(0) : 0; is: temp.d(11): Error: template std.traits.isNumeric cannot deduce function from argument types !()(string), candidates are:
Re: How to avoid throwing an exceptions for a built-in function?
On Thursday, 11 May 2017 at 19:59:55 UTC, Jordan Wilson wrote: On Thursday, 11 May 2017 at 18:07:47 UTC, H. S. Teoh wrote: On Thu, May 11, 2017 at 05:55:03PM +, k-five via Digitalmars-d-learn wrote: On Thursday, 11 May 2017 at 17:18:37 UTC, crimaniak wrote: > On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote: - This reason is why I sometimes use isNumeric if I have heaps of strings I need to convert, to reduce exceptions. So something like: int index = (str.isNumeric) ? to!int(str).ifThrown(0) : 0; Jordan -- Interesting! I was worried about performance and for that I did not want to use try-catch. So (isNumberic) is a good solution. http://dlang.org/phobos/std_traits.html#isNumeric
Re: How to avoid throwing an exceptions for a built-in function?
On Thursday, 11 May 2017 at 18:07:47 UTC, H. S. Teoh wrote:
On Thu, May 11, 2017 at 05:55:03PM +, k-five via
Digitalmars-d-learn wrote:
On Thursday, 11 May 2017 at 17:18:37 UTC, crimaniak wrote:
> On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
-
> try this:
> https://dlang.org/phobos/std_exception.html#ifThrown
Worked. Thanks.
import std.stdio;
import std.conv: to;
import std.exception: ifThrown;
void main( string[] args ){
string str = "string";
int index = to!int( str ).ifThrown( 0 ); // if an exception
was thrown, it
is ignored and then return ( 0 );
writeln( "index: ", index ); // 0
}
Keep in mind, though, that you should not do this in an inner
loop if you care about performance, as throwing / catching
exceptions will incur a performance hit. Outside of inner
loops, though, it probably doesn't matter.
T
This reason is why I sometimes use isNumeric if I have heaps of
strings I need to convert, to reduce exceptions. So something
like:
int index = (str.isNumeric) ? to!int(str).ifThrown(0) : 0;
Jordan
Re: How to avoid throwing an exceptions for a built-in function?
On Thu, May 11, 2017 at 05:55:03PM +, k-five via Digitalmars-d-learn wrote:
> On Thursday, 11 May 2017 at 17:18:37 UTC, crimaniak wrote:
> > On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
> -
> > try this:
> > https://dlang.org/phobos/std_exception.html#ifThrown
>
>
>
> Worked. Thanks.
>
> import std.stdio;
> import std.conv: to;
> import std.exception: ifThrown;
>
> void main( string[] args ){
>
> string str = "string";
> int index = to!int( str ).ifThrown( 0 ); // if an exception was thrown,
> it
> is ignored and then return ( 0 );
> writeln( "index: ", index );// 0
> }
Keep in mind, though, that you should not do this in an inner loop if
you care about performance, as throwing / catching exceptions will incur
a performance hit. Outside of inner loops, though, it probably doesn't
matter.
T
--
Ph.D. = Permanent head Damage
Re: How to avoid throwing an exceptions for a built-in function?
On Thursday, 11 May 2017 at 17:18:37 UTC, crimaniak wrote:
On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
-
try this:
https://dlang.org/phobos/std_exception.html#ifThrown
Worked. Thanks.
import std.stdio;
import std.conv: to;
import std.exception: ifThrown;
void main( string[] args ){
string str = "string";
int index = to!int( str ).ifThrown( 0 ); // if an exception was
thrown, it is ignored and then return ( 0 );
writeln( "index: ", index ); // 0
}
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
I have a line of code that uses "to" function in std.conv for a
purpose like:
int index = to!int( user_apply[ 4 ] ); // string to int
When the user_apply[ 4 ] has value, there is no problem; but
when it is empty: ""
it throws an ConvException exception and I want to avoid this
exception.
currently I have to use a dummy catch:
try{
index = to!int( user_apply[ 4 ] );
} catch( ConvException conv_error ){
// nothing
}
I no need to handle that, so is there any way to prevent this
exception?
try this:
https://dlang.org/phobos/std_exception.html#ifThrown
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 21:44:32 UTC, Andrei Alexandrescu
wrote:
On 5/10/17 3:40 PM, k-five wrote:
---
I no need to handle that, so is there any way to prevent this
exception?
Use the "parse" family:
https://dlang.org/phobos/std_conv.html#parse -- Andrei
---
This is my answer :). I want a way to covert a string without
facing any exceptions.
But may I do not understand so well the documentation
It says:
The parse family of functions works quite like the to family,
except that:
1 - It only works with character ranges as input.
2 - It takes the input by reference. (This means that rvalues
- such as string literals - are not accepted: use to instead.)
3 - It advances the input to the position following the
conversion.
4 - It does not throw if it could not convert the entire
input.
here, number 4: It does not throw if it could not convert the
entire input.
then it says:
Throws:
A ConvException if the range does not represent a bool.
Well it says different things about throwing!
Also I tested this:
import std.stdio;
import std.conv: parse;
void main( string[] args ){
string str = "string";
int index = parse!int( str );
writeln( "index: ", index );
}
the output:
std.conv.ConvException@/usr/include/dmd/phobos/std/conv.d(2111):
Unexpected 's' when converting from type string to type int
and so on ...
Please correct me if I am wrong.
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 21:19:21 UTC, Stanislav Blinov wrote:
On Wednesday, 10 May 2017 at 15:35:24 UTC, k-five wrote:
On Wednesday, 10 May 2017 at 14:27:46 UTC, Stanislav Blinov
---
I don't understand. If you don't want to take care of
exceptions, then you just don't do anything, simply call
to!int(str).
Well I did that, but when the string is a valid type like: "10"
there is no problems. But when the string is not valid, like:
"abc", then to! function throws an exception.
Why I do not want to take care of that? Because I just need the
value, if the string is valid, otherwise no matter what the value
of string is.
First I just wrote:
index = to!int( user_apply[ 4 ] );
And this code is a part of a command-line program and the user
may enter anything. So, for a valid string:
./program '10' // okey
but for:
./program 'non-numerical' // throws an exception an 10 lines of
error appear on the screen( console )
I just want to silent this exception. Of course it is useful for
handling when someone wants to. But in my code I no need to
handle it. So I want to silent that, without using try{}catch(){}
block. I just wondered about try-catch and I want to know may
there would be a better way instead of a dummy try-catch block.
Thanks for replying and mentioning. And I am sorry, since I an
new in English Writing, if you got confuse.
Re: How to avoid throwing an exceptions for a built-in function?
On 05/10/2017 05:40 AM, k-five wrote:
> I have a line of code that uses "to" function in std.conv for a purpose
> like:
>
> int index = to!int( user_apply[ 4 ] ); // string to int
>
> When the user_apply[ 4 ] has value, there is no problem; but when it is
> empty: ""
> it throws an ConvException exception and I want to avoid this exception.
>
> currently I have to use a dummy catch:
> try{
> index = to!int( user_apply[ 4 ] );
> } catch( ConvException conv_error ){
> // nothing
> }
Are you really fine with 'index' being left with its previous value? If
so, you can write a function like the following:
void setMaybe(To, From)(ref To var, From from) {
import std.conv : to, ConvException;
try {
var = to!To(from);
} catch( ConvException conv_error ) {
}
}
unittest {
int index = 41;
index.setMaybe("42");
assert(index == 42);
index.setMaybe("forty three");
assert(index == 42);
index.setMaybe("");
assert(index == 42);
}
void main() {
}
If you want the variable to be set to a default value (perhaps .init),
then here is an idea:
void setMaybe(To, From)(ref To var, From from, To def = To.init) {
import std.conv : to, ConvException;
try {
var = to!To(from);
} catch( ConvException conv_error ) {
var = def;
}
}
unittest {
int index = 41;
index.setMaybe("42");
assert(index == 42);
index.setMaybe("forty three");
assert(index == 0);
index.setMaybe(7);
index.setMaybe("", 8);
assert(index == 8);
}
void main() {
}
Ali
Re: How to avoid throwing an exceptions for a built-in function?
On 5/10/17 3:40 PM, k-five wrote:
I have a line of code that uses "to" function in std.conv for a purpose
like:
int index = to!int( user_apply[ 4 ] ); // string to int
When the user_apply[ 4 ] has value, there is no problem; but when it is
empty: ""
it throws an ConvException exception and I want to avoid this exception.
currently I have to use a dummy catch:
try{
index = to!int( user_apply[ 4 ] );
} catch( ConvException conv_error ){
// nothing
}
I no need to handle that, so is there any way to prevent this exception?
Use the "parse" family: https://dlang.org/phobos/std_conv.html#parse --
Andrei
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 21:19:21 UTC, Stanislav Blinov wrote: "nothrow" does not turn off exceptions, it simply forbids throwing them in the enclosing scope (i.e. calling anything that might throw is not allowed). nothrow disallows the function scope to throw exceptions not derived from core.object.Error. It makes no claim about what happens *inside* the scope; you can throw as much as you want inside nothrow, as long as you take care to catch anything that's not a core.object.Error (which is what std.exception.assumeWontThrow essentially does).
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 15:35:24 UTC, k-five wrote:
On Wednesday, 10 May 2017 at 14:27:46 UTC, Stanislav Blinov
wrote:
On Wednesday, 10 May 2017 at 13:27:17 UTC, k-five wrote:
Thanks, but I know about what are you saying. The
user_apply[4] has so many possibilities and I cannot use
if-else
That doesn't sound right. Either you've already handled all
the possible cases and thus expect the to! to not throw (can
specify that i.e. via std.exception.assumeWontThrow), or, as
you're saying, it's much more than an if-else, but in that
case exception will be thrown on invalid input.
--
I know. But I am saying that I do not want to take care of any
exceptions.
I just wanted to write:
int variable = to!int( string-type );
In fact something like using "no throw" is a function:
void init( ... ) nothrow {
...
int variable = to!int( string-type );
...
}
but this is not valid.
Thanks anyway and I will test: Function
std.exception.assumeWontThrow at this link:
https://dlang.org/library/std/exception/assume_wont_throw.html
I don't understand. If you don't want to take care of exceptions,
then you just don't do anything, simply call to!int(str). If an
exception is thrown, it'll propagate further up the stack, until
you either handle it or abort the program. "nothrow" does not
turn off exceptions, it simply forbids throwing them in the
enclosing scope (i.e. calling anything that might throw is not
allowed).
Or do you mean that you've already made sure that the user input
is valid such that to!int() will never throw with it? In that
case, yes, assumeWontThrow is a way to express that. But then,
the only way you can be sure of that is if you've already parsed
the input yourself, so I'm not clear on the intent.
Alternatively, if what you're calling still might throw but you
don't want to deal with try/catch blocks, there's
collectException function in std.exception that'll give you the
exception if it was thrown and let you deal with it without using
try/catch.
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 14:27:46 UTC, Stanislav Blinov wrote:
On Wednesday, 10 May 2017 at 13:27:17 UTC, k-five wrote:
Thanks, but I know about what are you saying. The
user_apply[4] has so many possibilities and I cannot use
if-else
That doesn't sound right. Either you've already handled all the
possible cases and thus expect the to! to not throw (can
specify that i.e. via std.exception.assumeWontThrow), or, as
you're saying, it's much more than an if-else, but in that case
exception will be thrown on invalid input.
--
I know. But I am saying that I do not want to take care of any
exceptions.
I just wanted to write:
int variable = to!int( string-type );
In fact something like using "no throw" is a function:
void init( ... ) nothrow {
...
int variable = to!int( string-type );
...
}
but this is not valid.
Thanks anyway and I will test: Function
std.exception.assumeWontThrow at this link:
https://dlang.org/library/std/exception/assume_wont_throw.html
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 13:27:17 UTC, k-five wrote: Thanks, but I know about what are you saying. The user_apply[4] has so many possibilities and I cannot use if-else That doesn't sound right. Either you've already handled all the possible cases and thus expect the to! to not throw (can specify that i.e. via std.exception.assumeWontThrow), or, as you're saying, it's much more than an if-else, but in that case exception will be thrown on invalid input.
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 13:12:46 UTC, Ivan Kazmenko wrote:
On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
--
I assume that an empty string is a valid input then.
The question is, what value do you want `index` to have when
the string is empty?
Maybe the old value, or some constant?
In any case, to better express your intent, you may write
something like:
if (user_apply[4] != "")
{
index = to !(int) (user_apply[4]);
}
else
{
index = ...; // specify whatever your intent is
}
This way, the code is self-documenting, and the program still
throws when `user_apply[4]` is neither empty nor an integer,
which may be the right thing to do in the long run.
Ivan Kazmenko.
--
Thanks, but I know about what are you saying. The user_apply[4]
has so many possibilities and I cannot use if-else
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
I have a line of code that uses "to" function in std.conv for a
purpose like:
int index = to!int( user_apply[ 4 ] ); // string to int
When the user_apply[ 4 ] has value, there is no problem; but
when it is empty: ""
it throws an ConvException exception and I want to avoid this
exception.
currently I have to use a dummy catch:
try{
index = to!int( user_apply[ 4 ] );
} catch( ConvException conv_error ){
// nothing
}
I no need to handle that, so is there any way to prevent this
exception?
I assume that an empty string is a valid input then.
The question is, what value do you want `index` to have when the
string is empty?
Maybe the old value, or some constant?
In any case, to better express your intent, you may write
something like:
if (user_apply[4] != "")
{
index = to !(int) (user_apply[4]);
}
else
{
index = ...; // specify whatever your intent is
}
This way, the code is self-documenting, and the program still
throws when `user_apply[4]` is neither empty nor an integer,
which may be the right thing to do in the long run.
Ivan Kazmenko.
Re: How to avoid throwing an exceptions for a built-in function?
On Wednesday, 10 May 2017 at 12:40:41 UTC, k-five wrote:
I have a line of code that uses "to" function in std.conv for a
purpose like:
int index = to!int( user_apply[ 4 ] ); // string to int
When the user_apply[ 4 ] has value, there is no problem; but
when it is empty: ""
it throws an ConvException exception and I want to avoid this
exception.
currently I have to use a dummy catch:
try{
index = to!int( user_apply[ 4 ] );
} catch( ConvException conv_error ){
// nothing
}
I no need to handle that, so is there any way to prevent this
exception?
there has been talk of adding an overload that substitutes a
supplied value on failure.
apart from that there is assumeWontThrow in the stdlib somewhere.
How to avoid throwing an exceptions for a built-in function?
I have a line of code that uses "to" function in std.conv for a
purpose like:
int index = to!int( user_apply[ 4 ] ); // string to int
When the user_apply[ 4 ] has value, there is no problem; but when
it is empty: ""
it throws an ConvException exception and I want to avoid this
exception.
currently I have to use a dummy catch:
try{
index = to!int( user_apply[ 4 ] );
} catch( ConvException conv_error ){
// nothing
}
I no need to handle that, so is there any way to prevent this
exception?
