• rumbu (18/18) Apr 05 2018 Is there a standard way to handle errors in a chain of range
• Timoses (14/35) Apr 05 2018 You could use predicates:
• Seb (5/8) Apr 05 2018 Are you aware of ifThrown?
• rumbu (2/11) Apr 05 2018 Thanks, ifThrown is perfect.

rumbu <rumbu rumbu.ro> writes:

Is there a standard way to handle errors in a chain of range 
transformations?

Let's say I want to read some comma separated numbers from a file.

auto myArray = file.byLine().splitter().map!(to!int).array();

Now, besides fatal errors (like I/O), let's suppose I want to 
handle some errors in a silent way:
- skip unicode decoding errors;
- assume blank records with 0;
- skip the line entirely if the conversion to int is not possible;

I can catch UTFException, ConvException or ConvOverflowException 
for the entire syntax chain but there are some disadvantages:
- I don't know exactly which of the chain members thrown the 
exception;
- I cannot skip/handle the error and continue;

The only solution I thought about is to break the nice chain 
syntax and handle errors on each of the chain members, but I 
wonder if there is probably another way.

Thanks.

Timoses <timosesu gmail.com> writes:

On Thursday, 5 April 2018 at 17:06:04 UTC, rumbu wrote:
 Is there a standard way to handle errors in a chain of range 
 transformations?

 Let's say I want to read some comma separated numbers from a 
 file.

 auto myArray = file.byLine().splitter().map!(to!int).array();

 Now, besides fatal errors (like I/O), let's suppose I want to 
 handle some errors in a silent way:
 - skip unicode decoding errors;
 - assume blank records with 0;
 - skip the line entirely if the conversion to int is not 
 possible;

 I can catch UTFException, ConvException or 
 ConvOverflowException for the entire syntax chain but there are 
 some disadvantages:
 - I don't know exactly which of the chain members thrown the 
 exception;
 - I cannot skip/handle the error and continue;

 The only solution I thought about is to break the nice chain 
 syntax and handle errors on each of the chain members, but I 
 wonder if there is probably another way.

 Thanks.

You could use predicates:

```
     string list = "3, 5, 1, , not a number, 100";

     int[] numbers = list.split(",").filter!((entry) {
         if (!isNumeric(entry.strip))
             return false;
         else // ... even more cases?
             return true;
     	})
         .map!((e) => e.strip.to!int).array;

     assert(numbers == [3, 5, 1, 100]);
```
https://run.dlang.io/gist/413282d9726dbac137bf5f35033a8eea

Seb <seb wilzba.ch> writes:

On Thursday, 5 April 2018 at 17:06:04 UTC, rumbu wrote:
 Is there a standard way to handle errors in a chain of range 
 transformations?

 [...]

Are you aware of ifThrown?

https://dlang.org/phobos/std_exception.html#ifThrown

It's not perfect, but imho a nice start and one of the places 
where lazy really shines.

rumbu <rumbu rumbu.ro> writes:

On Thursday, 5 April 2018 at 17:36:56 UTC, Seb wrote:
 On Thursday, 5 April 2018 at 17:06:04 UTC, rumbu wrote:
 Is there a standard way to handle errors in a chain of range 
 transformations?

 [...]

 Are you aware of ifThrown?

 https://dlang.org/phobos/std_exception.html#ifThrown

 It's not perfect, but imho a nice start and one of the places 
 where lazy really shines.

Thanks, ifThrown is perfect.