On Monday, 17 March 2014 at 13:04:36 UTC, Mike wrote:
Consider the following silly, but illustrative example:
***********************************************
mixin template HasValue(ContainingType)
{
uint value = ContainingType.outerValue;
}
struct MyStruct
{
uint outerValue;
mixin HasValue!(typeof(this));
}
***********************************************
Now what if I wanted to use that mixin in a module:
***********************************************
module myModule;
uint outerValue;
mixin HasValue!(typeof({what?}); //how do I refer to the
module type
there is no 'this' for
modules
************************************************
Basic question: How can I have my mixin refer to the type it's
mixing into, and have it work regardless of whether it's mixing
into a module or a class/struct?
Modules aren't types.
Templates can have different kinds of parameters[1]:
* Type parameters take types. That means, modules are out.
* Alias parameters take symbols, e.g. user defined types (e.g.
MyStruct) and modules (e.g. myModule), but not built-in types
(e.g. int).
* Tuple parameters take any amount of anything the other
parameter variants accept.
* Value parameters and this parameters are not of interest here.
So, when you need to accept built-in types, you have to go with a
tuple parameter. Otherwise, an alias parameter works, too.
With a tuple parameter:
---
mixin template HasValue(context ...) if(context.length == 1)
{
uint value = context[0].outerValue;
}
---
The alias parameter version is a bit simpler:
---
mixin template HasValue(alias context)
{
uint value = context.outerValue;
}
---
[1] http://dlang.org/template#TemplateParameter
