Limitations on parameters for structs/functions.

[benjamin-macadam]

I don't understand the limitations of parameters for structs/functions. For example, if I wanted to have a ShapedArray type, similar to Julia's StaticArrays, I would want to have a rank parameter giving the shape of the dimensions tuple and the shape tuple as parameters. From what I can tell, you get something like this:

from Index import StaticIntTuple, product
from DType import DType
from Pointer import DTypePointer
from Random import rand, random_f64

struct StaticSizedArray[dtype: DType, rank: Int, dims: StaticIntTuple[rank]]:
    var data: DTypePointer[dtype]
    var size: Int
    
    def __init__(inout self):
        self.size = product(dims, rank)
        self.data = DTypePointer[dtype].alloc(self.size)
        rand(self.data, self.size)

However, this doesn't seem to play nicely with Mojo, as I get the following error:

error: Expression [14]:6:1: no viable expansions found
fn __lldb_expr__(inout __mojo_repl_arg: __mojo_repl_context__):
^

Expression [14]:8:28:   call expansion failed
    __mojo_repl_expr_impl__(__mojo_repl_arg)
                           ^

Expression [14]:12:1:     no viable expansions found
def __mojo_repl_expr_impl__(inout __mojo_repl_arg: __mojo_repl_context__) -> None:
^

Expression [14]:20:26:       call expansion failed
  __mojo_repl_expr_body__()
                         ^

Expression [14]:14:3:         no viable expansions found
  def __mojo_repl_expr_body__() -> None:
  ^

Expression [14]:17:69:           failed to evaluate 'apply'
    var s = StaticSizedArray[DType.f32, 3, StaticIntTuple[3](3,3,4)]()
                                                                    ^

/.modular/Kernels/mojo/Stdlib/Index.mojo:206:5:             failed to interpret function @$Index::StaticIntTuple::__init__($Int::Int*),size=3
    fn __init__(*elems: Int) -> Self:
    ^

/.modular/Kernels/mojo/Stdlib/Index.mojo:228:9:               failed to fold operation pop.compiler.global_store(#pop.struct<[3, 3, 4], #M.pointer<268435456>> : !pop.struct<!kgen.variadic<!pop.scalar<index>>, pointer<array<3, scalar<index>>>>)
        fn body[idx: Int]():

Whereas if I remove that dependency, things seem to work fine:

struct StaticDimArray[dtype: DType, rank: Int]:
    var data: DTypePointer[dtype]
    var shape: StaticIntTuple[rank]
    var size: Int
    
    def __init__(inout self, shape: StaticIntTuple[rank]):
        self.shape = shape
        self.size = product(self.shape, rank)
        self.data = DTypePointer[dtype].alloc(self.size)
        rand(self.data, self.size)

var s = StaticDimArray[DType.f32, 3](StaticIntTuple[3](3,3,4))

doesn't run into any issues.

[lattner]

I'm not sure what is going on here either - this works fine on the command line, and anything complaining about __lldb_expr__ is likely due to the notebook integration support. That said, I don't see any top level code. Is your example complete or did you omit something?