My template tuple code does not compile

[Victor Porton]

I rewrote it again:

https://github.com/vporton/struct-params-dlang/blob/f50f7e5919f90b1d06bf0cc08e3055548aad1797/source/struct_params.d

But it does not work :-( What is my error?

source/struct_params.d(43,60): Error: function expected before 
`()`, not `()` of type `()`
source/struct_params.d(44,43): Error: undefined identifier 
`fieldsWithDefaults`
source/struct_params.d(56,11): Error: template instance 
`struct_params.ProviderParamsCode!("S", int, "x", float, "y")` 
error instantiating
source/struct_params.d(82,5): Error: mixin 
`struct_params.__unittest_L81_C1.ProviderParams!("S", int, "x", 
float, "y")` error instantiating