What's wrong with parameters? Are you making life harder for yourself than you
need to? :-)
If you're worried about the (very slight) overhead (isleaftype calls out to C,
and therefore can't be inlined), then you could use a Union where you specify
all the types you allow. Or define the following function:
fastleaftype{T}(::Type{T}) = error("Must be a concrete type")
for x in names(Core)
T = eval(x)
if isleaftype(T) && T <: Number
@eval begin
fastleaftype(::Type{$T}) = nothing
end
end
end
Then:
function myfunction(x::Array)
fastleaftype(eltype(x))
x .+ 1
end
Now check this out:
julia> code_typed(myfunction, (Matrix{Float64},))
1-element Array{Any,1}:
:($(Expr(:lambda, {:x}, {{},{{:x,Array{Float64,2},0}},{}}, :(begin # none,
line 2:
nothing # line 3:
return x::Array{Float64,2} .+ 1::Array{Float64,2}
end::Array{Float64,2}))))
julia> code_typed(myfunction, (Matrix{Real},))
1-element Array{Any,1}:
:($(Expr(:lambda, {:x}, {{},{{:x,Array{Real,2},0}},{}}, :(begin # none, line
2:
throw($(Expr(:new, :(top(getfield)
(Base,:ErrorException)::Type{ErrorException}), "Must be a concrete
type"))::ErrorException)::None # line 3:
return x::Array{Real,2} .+ 1::Array{Real,2}
end::Array{Real,2}))))
The compiler does the check for you, and this adds nothing whatsoever to your
runtime.
--Tim
On Wednesday, April 30, 2014 07:37:05 AM Oliver Woodford wrote:
> On Wednesday, April 30, 2014 3:20:23 PM UTC+1, Tim Holy wrote:
> > You can add this as the first line of your function:
> > assert_leaftype(T)
> >
> > where
> >
> > assert_leaftype(T) = isleaftype(T) || error("Must be a concrete type")
> >
> > To your users, this is at least as useful as
> >
> > ERROR: no method myfunction(Array{Real,1})
> >
> > which is what it would be if you relied on method dispatch to generate the
> > error (which is what I think you're asking for).
> >
> > --Tim
>
> It's OK, but it still requires me to have a static parameter. Is there a
> O(1) time solution which avoids the need for static parameters. Something
> like:
>
> function frob(x::Array)
> isleaftype(x) || error("Homogeneous array required")
>
> though I know this won't work.
