What's the purpose of the 'in' keyword ?

[rikki cattermole]

On 28/05/2018 1:02 AM, loloof64 wrote:
> Hello everyone,
> 
> I've just completed the language tour, and I am starting a tutorial in 
> order to use Gtk binding.
> 
> But somewhere, they use the 'in' keyword for the constructor : 
> (https://sites.google.com/site/gtkdtutorial/#chapter2 : in section 3 for 
> Buttons and Callbacks, main.d snippet).
> 
> What's the purpose of this 'in' keyword ? I could not process a good 
> Google request to get an answer.
> 
> Regards

https://dlang.org/spec/function.html#parameters