nothrow and std.exception.ifThrown

[novice2]

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.