confused about string and lambda args

[Adam D. Ruppe]

On Thursday, 16 January 2020 at 17:03:33 UTC, mark wrote:
>     auto wordCharCounts = words // I added this and it works 
> fine
>         .map!"a.length";
>     writeln(wordCharCounts);

The string thing probably shouldn't be used anymore. I suggest 
you always use the => form instead.

The string thing is a legacy version that was before the language 
had =>.

> I don't understand why both syntaxes work for .length but only 
> the string form for .count?

It is because of imports.

So the string version passes the string to the library, which 
pastes it into some skeleton code and makes a function out of it.

It basically does:

     string code = "import some_stuff; (a) { return " ~ 
your_string ~ "; }";
     mixin(code);

Note it does this INSIDE the library.

It is that `import some_stuff;` that accounts for this 
difference. The string one pastes in some library imports so some 
functions are available. The => form does not.

Since the string one is inside the lib, it can NOT see your own 
functions from your module! But since the lib imports a few other 
library modules, it may be able to see things your module didn't 
import.

The better way to do it is to use your => format, but go ahead 
and import the necessary module.

I believe `count` is located in `import std.algorithm;`. So add 
that to your module and it should work now.