ADL

[ZombineDev via Digitalmars-d]

On Saturday, 3 September 2016 at 10:56:20 UTC, Tobias M wrote:
> On Saturday, 3 September 2016 at 10:33:22 UTC, Walter Bright 
> wrote:
>> I don't think it is a template issue. It's a name lookup 
>> issue. There's LINQ in C#, for example.
>
> I think it is.
>
> The problem is lookup of dependent symbols (see C++ two phase 
> lookup). Without real templates, all lookup can be done at 
> definition time.
> I'm not very familiar with LINQ, but generally C# uses uses 
> interfaces as constraints on generics, similar to traits/type 
> classes. Lookup is then done once, considering only the 
> interfaces, not for each the concrete type.

No, LINQ doesn't work because of interfaces, but because of 
extension methods (C#'s variant of UFCS). The IEnumerable<T> 
interface defines only a single method. All the useful 
functionality is implemented as extension methods which are only 
available if the user specifically imports the namespace in which 
where they're defined (just like D's ranges and range primitive 
implementations for arrays). Those extension methods are used as 
a fallback, similarly to UFCS in D: every type can override the 
extension methods by implementing the method itself. Also more 
inner namespaces (more closer to the method invocation) override 
more outer namespaces. For more info see:

1) 
https://github.com/ljw1004/csharpspec/blob/gh-pages/expressions.md#member-lookup Member Lookup
2) 
https://github.com/ljw1004/csharpspec/blob/gh-pages/expressions.md#member-access Member access and
3) 
https://github.com/ljw1004/csharpspec/blob/gh-pages/expressions.md#extension-method-invocations Extension method invocations