On Thursday, 29 April 2021 at 16:02:20 UTC, novice2 wrote:
Hello.
I need use std.format.format() in nothrow function.
format() can throw.
For this case i have special default string.
I don't want embrace format into try..catch block,
and i found elegant std.exception.ifThrown.
But DMD say "ifThrown not nothrow"
https://run.dlang.io/is/kXtt5q
```d
nothrow string foo(int x, string def) {
import std.format: format;
import std.exception: ifThrown;
return format("%d", x).ifThrown(def);
}
Error: function std.exception.ifThrown!(Exception, string,
string).ifThrown is not nothrow
```
What i can use instead of ifThrown, or how it can be changed to
nothrow?
Thanks.
The reason for this, apparently, is in the definition of
`ifThrown`:
```
CommonType!(T1, T2) ifThrown(E : Throwable = Exception, T1,
T2)(lazy scope T1 expression, lazy scope T2 errorHandler) nothrow
```
It's not marked as `nothrow` in the function's definition, so
even if the delegate passed to ifThrown _is_ nothrow, the
compiler can't tell. There's no easy way around this that I can
think of OTOH that doesn't involve some effort on your part. One
thing you can do is wrap ifThrown with
`std.exception.assumeWontThrow`:
```
import std.exception: ifThrown, assumeWontThrow;
import std.functional: pipe;
alias ifThrown = pipe!(std.exception.ifThrown, assumeWontThrow);
nothrow string foo(int x, string def) nothrow {
import std.format: format;
return format("%d", x).ifThrown(def);
}
```
