The code:

string s = "...";
if(s.isNumeric){
    auto x = parse!int(s); // Can I be sure here that parse will
not throw?
}

On Thursday, 20 February 2014 at 19:11:55 UTC, Cooler wrote:
> The code:
>
> string s = "...";
> if(s.isNumeric){
>     auto x = parse!int(s); // Can I be sure here that parse will
> not throw?
> }

No. s may still contain data that is not convertible to int. For
example, "nan".

On Thursday, 20 February 2014 at 19:18:15 UTC, Stanislav Blinov
wrote:
> On Thursday, 20 February 2014 at 19:11:55 UTC, Cooler wrote:
>> The code:
>>
>> string s = "...";
>> if(s.isNumeric){
>>    auto x = parse!int(s); // Can I be sure here that parse will
>> not throw?
>> }
>
> No. s may still contain data that is not convertible to int. For
> example, "nan".

Is there any way to know that a string is convertible to a number
without throwing?

Cooler:

> Is there any way to know that a string is convertible to a number without throwing?

I suggested to add it:
https://d.puremagic.com/issues/show_bug.cgi?id=6840

Bye,
bearophile

On Thursday, 20 February 2014 at 19:23:28 UTC, Cooler wrote:
> On Thursday, 20 February 2014 at 19:18:15 UTC, Stanislav Blinov
> wrote:
>> On Thursday, 20 February 2014 at 19:11:55 UTC, Cooler wrote:
>>> The code:
>>>
>>> string s = "...";
>>> if(s.isNumeric){
>>>   auto x = parse!int(s); // Can I be sure here that parse will
>>> not throw?
>>> }
>>
>> No. s may still contain data that is not convertible to int. For
>> example, "nan".
>
> Is there any way to know that a string is convertible to a number
> without throwing?

You could do this.

import std.stdio;
import std.algorithm: all;
import std.ascii: isDigit;

void main(string[] args) {
     writeln("123".all!isDigit); // true
     writeln("12x".all!isDigit); // false
}

Combine the "all" algorithm which returns true if everything in a
range matches a predicate and use "isDigit" as the predicate
which returns true if the character is an ascii digit.

if (s.length > 0 && s.all!isDigit) {
     // Never throws now.
     auto x = parse!int(s);
}

On Thursday, 20 February 2014 at 19:46:35 UTC, w0rp wrote:

> if (s.length > 0 && s.all!isDigit) {
>      // Never throws now.
>      auto x = parse!int(s);
> }

And what about +/- and U/L suffixes? Or, say, different base (i.e. hexadecimal)?

It would be way more beneficial if Phobos' parse (or some additional function) returned some kind of Optional. Maybe a D implementation of Andrei's Expected<T>?

On Thursday, 20 February 2014 at 19:58:10 UTC, Stanislav Blinov
wrote:
> On Thursday, 20 February 2014 at 19:46:35 UTC, w0rp wrote:
>
>> if (s.length > 0 && s.all!isDigit) {
>>     // Never throws now.
>>     auto x = parse!int(s);
>> }
>
> And what about +/- and U/L suffixes? Or, say, different base (i.e. hexadecimal)?
>
> It would be way more beneficial if Phobos' parse (or some additional function) returned some kind of Optional. Maybe a D implementation of Andrei's Expected<T>?

True, this doesn't cover those. Returning a
Maybe/Option/Nullable/Whatever type from another function may be
better.

On Thursday, 20 February 2014 at 19:37:08 UTC, bearophile wrote:
> Cooler:
>
>> Is there any way to know that a string is convertible to a number without throwing?
>
> I suggested to add it:
> https://d.puremagic.com/issues/show_bug.cgi?id=6840
>
> Bye,
> bearophile

Yeap. Thanks. Will wait for the enhancment.

On Thursday, 20 February 2014 at 19:46:35 UTC, w0rp wrote:
> if (s.length > 0 && s.all!isDigit) {
>      // Never throws now.
>      auto x = parse!int(s);
> }

Nope, integer overflow exception. Though I didn't check if it would actually through that, but it should.