Why can I call a function with mismatched parameter type?

[rikki cattermole]

string is not a built in type. It is an alias defined by druntime.

https://github.com/dlang/druntime/blob/master/src/object.d#L35

int on the other hand is defined by the compiler. It understands it.

Further, when the parameter name is not provided it will infer based 
upon what is passed in. In effect it is templated.