What does func!thing mean?

[qznc]

On Friday, 8 November 2013 at 05:46:29 UTC, ProgrammingGhost 
wrote:
> I'm a D noob. ".map!(a => a.length)" seems like the lambda is 
> passed into the  template. ".map!split" just confuses me. What 
> is split? I thought only types can be after "!". I would guess 
> split is a standard function but then shouldn't it be 
> map!(split)?
>
>     const wordCount = file.byLine()                  // Read 
> lines
>                           .map!split                 // Split 
> into words
>                           .map!(a => a.length)       // Count 
> words per line
>                           .reduce!((a, b) => a + b); // Total 
> word count

Do you know C++ templates? C++ func<thing> == D func!(thing).

You can pass anything into a template, not just types. So you are 
right, "map!split" gives the "split" function into the "map" 
template and "map!(split)" is the canonical form. D allows you to 
remove the parens for simple cases, hence "map!split".