Orphan format arguments: args[0..1]

[bauss]

On Sunday, 16 December 2018 at 00:34:48 UTC, Ali Çehreli wrote:
> This one confused me until I decided to talk to a rubber ducky:
>
> import std.string;
>
> void main() {
>     auto s = "%s is a good number".format(42);
> }
>
> Fine; it works... Then the string becomes too long and I split 
> it:
>
>     auto s = "%s is a good number but one needs to know" ~
>              " what the question exactly was.".format(42);
>
> Now there is a compilation error:
>
>   Orphan format arguments: args[0..1]
>
> What? Is that a bug in format? It can't be because the string 
> should be concatenated by the compiler as a single string, no? 
> No: operator dot has precedence over ~, so format is applied to 
> the second part of the string before the concatenation. Doh! 
> This puzzled me a lot.
>
> Anyway, the solution, once again, is to use parentheses:
>
>     auto s = ("%s is a good number but one needs to know" ~
>               " what the question exactly was.").format(42);
>
> Ali

The reason it doesn't work in the second example is because it 
translates to something like this:

auto s = "%s is a good number but one needs to know" ~ ("what the 
question exactly was.".format(42));

The reason encapsulation the two strings works is because you 
append the second string to the first before you call format.

Definitely not a bug.