How do you put log calls in constructors when they may be created in a static context?

[aliak]

On Wednesday, 8 August 2018 at 23:47:22 UTC, Jonathan M Davis 
wrote:
> On Wednesday, August 8, 2018 3:54:34 PM MDT aliak via 
> Digitalmars-d-learn wrote:
>> I'm trying to debug stuff, so I want to add verbose logging
>>
>> struct S(T) {
>>    this() {
>>      writeln("created S(T) with properties and ID");
>>    }
>> }
>>
>> static a = S!int(); // bah
>>
>> I guess users can call this code from any context, but when 
>> i'd also like to see the log output for debugging purposes. Is 
>> there a way around this?
>>
>> Can I maybe only do a writeln in a non compile-time context?
>
> if(__ctfe)
> {
>     // code here will execute if this is encountered during CTFE
> }
> else
> {
>     // code here will execute if this is encountered outside of 
> CTFE
> }
>
> - Jonathan M Davis

That won't work because __ctfe is not readable at compile time. 
And I don't want that writeln there when there's compile time 
evaluation because errors.

1) I want to be able to log when a type is created
2) I want to declare a locally static runtime type

Ie:

import std.stdio;

struct S(T) {
     T i;
     this(T i) {
         this.i = i;
         writeln("log it");
     }
}

int f() {
     static x = S!int(3);
     return x.i++;
}

void main() {
     writeln(f); // print 3
     writeln(f); // print 4
}