Pointer to environment.get

[Basile B.]

On Monday, 28 August 2023 at 10:20:14 UTC, Basile B. wrote:
> On Monday, 28 August 2023 at 06:38:50 UTC, Vino wrote:
>> Hi All,
>>
>>   The the below code is not working, hence requesting your 
>> help.
>>
>> Code:
>> ```
>> import std.stdio;
>> import std.process: environment;
>> void main () {
>>    int* ext(string) = &environment.get("PATHEXT");
>>    writeln(*ext);
>> }
>> ```
>
> Problems is that "PATHEXT" is a runtime argument. If you really 
> want to get a pointer to the function for that runtime argument 
> you can use a lambda:
>
> ```d
> import std.stdio;
> import std.process: environment;
> void main () {
>
>     alias atGet = {return environment.get("PATHEXT");}; // 
> really lazy
>
>     writeln(atGet);         // pointer to the lambda
>     writeln((*atGet)());    // call the lambda
> }
> ```
>
> There might be other ways, but less idiomatic (using a struct + 
> opCall, a.k.a  a "functor")

To go further, the correct code for syntax you wanted to use is 
actually

```d
alias Ext_T = string (const char[] a, string b); // define a 
function type
alias Ext_PT = Ext_T*; // define a function **pointer** type
Ext_PT ext = &environment.get;
```

But as you can see that does not allow to capture the argument. 
Also it only work as AliasDeclaration RHS.