We need to talk about error messages of functions that are passed into other functions at compile time

[maik klein via Digitalmars-d]

I really like D's syntax for lambdas and I usually write code 
like this

   auto v = validationLayers[].all!((layerName){
     return layerProps[].count!((layer){
       return strcmp(cast(const(char*))layer.layerName, layerName) 
== 0;
     }) > 0;
   });

But this gives you basically 0 helpful error messages:


"Error: template 
breeze.graphics.context.createContext.all!((layerName)
{
return layerProps[].count!((layer)
{
return strcmp(cast(const(char*))layer.layerName, layerName) == 0;
}
) > 0;
}
).all cannot deduce function from argument types 
!()(const(char*)[]), candidates are:
/usr/include/dmd/phobos/std/algorithm/searching.d(113,10):        
breeze.graphics.context.createContext.all!((layerName)
{
return layerProps[].count!((layer)
{
return strcmp(cast(const(char*))layer.layerName, layerName) == 0;
}
) > 0;
}
).all(Range)(Range range) if (isInputRange!Range && 
is(typeof(unaryFun!pred(range.front))))
dmd failed with exit code 1"

For example I simply forgot to import `count`, nothing in the 
error message is really helpful and the only way to know for sure 
is to rip the function apart, which is not a very fun thing to do.

You can't also rip it apart easily because in the case above I 
implicitly capture `layerName` in the closure for `count`.

What are you thoughts on this?