D import idiom compilation time

[Dgame]

On Saturday, 5 January 2019 at 21:36:10 UTC, Neia Neutuladh wrote:
> On Sat, 05 Jan 2019 21:14:37 +0000, Dgame wrote:
>> I'm curious about that. Would that work or did I miss 
>> something?
>
> In your version, I might write:
>
>   from.std.stdio.thisFunctionDoesNotExist("Hallo");
>
> And the error I would get is:
>
>   Error: struct FromImpl does not overload ()

True.. What about:

----
template isModuleImport(string import_)
{
     enum isModuleImport = __traits(compiles, { mixin("import ", 
import_, ";"); });
}

template isSymbolInModule(string module_, string symbol)
{
     static if (isModuleImport!module_) {
         enum import_ = module_ ~ ":" ~ symbol;
         enum isSymbolInModule = __traits(compiles, { 
mixin("import ", import_, ";"); });
     } else {
         enum isSymbolInModule = false;
     }
}

template FailedSymbol(string symbol, string module_)
{
     auto FailedSymbol(Args...)(auto ref Args args)
     {
         assert(0, "Symbol \"" ~ symbol ~ "\" not found in " ~ 
module_);
     }
}

struct FromImpl(string module_)
{
     template opDispatch(string symbol)
     {
         static if (isSymbolInModule!(module_, symbol)) {
             mixin("import ", module_, "; alias opDispatch = ", 
symbol, ";");
         } else {
             static if (module_.length == 0) {
             	enum opDispatch = FromImpl!(symbol)();
             } else {
                 enum import_ = module_ ~ "." ~ symbol;
                 static if (isModuleImport!import_) {
                		enum opDispatch = FromImpl!(import_)();
                 } else {
                     alias opDispatch = FailedSymbol!(symbol, 
module_);
                 }
             }
         }
     }
}

enum from = FromImpl!null();

void main()
{
     from.std.stdio.writeln("Hallo");
     auto _ = from.std.datetime.stopwatch.AutoStart.yes;
     from.std.stdio.thisFunctionDoesNotExist("Hallo");
     from.std.stdio.thisFunctionDoesNotExist(42);
}
----

Output:

----
Hallo
core.exception.AssertError at onlineapp.d(20): Symbol 
"thisFunctionDoesNotExist" not found in std.stdio
----------------
??:? _d_assert_msg [0x3c00dc54]
onlineapp.d:20 pure nothrow @nogc @safe void 
onlineapp.FailedSymbol!("thisFunctionDoesNotExist", 
"std.stdio").FailedSymbol!(immutable(char)[]).FailedSymbol(immutable(char)[]) [0x3c00ceac]
onlineapp.d:52 _Dmain [0x3c00c8c3]
----