why can i define this function? julia> f(y,x...)=+(x...).*y f (generic function with 1 method) and can’t I define this other one? julia> f1(x...,y)=+(x...).*y ERROR: syntax: invalid "..." on non-final Couldn’t we gnisrap the arguments in reverse order? I guess there are many possible side eff…

This seems to be about slurping, not about optional arguments. Here’s a PR that addresses this: https://github.com/JuliaLang/julia/pull/42902 Not sure when/if it will land. But currently, this is not allowed.

Note that the PR doesn’t address method dispatch as the OP asked for. That would require changes to the type system to actually be able to represent signatures like this.

[image] rocco_sprmnt21: why can i define this function? julia> f(y,x...)=+(x...).*y The type signature of f is representable with Tuple{Any, Vararg} in Julia’s type system. In detail: Any is for y::Any, Vararg is for x::Vararg. [image] rocco_sprmnt21: and can’t I define this other one? …

Even putting aside overhauling the type system to accommodate non-trailing variadic arguments, it just doesn’t make sense. Right now, an input sequence first specifies the non-optional arguments, then fills in for as many optional arguments as possible, then any remaining could be slurped, all while…

Slurping on non-final argument

Internals & Design

mbaz April 8, 2022, 2:14pm 2

See this thread: Optional positional arguments must occur at end - #13 by Jean_Michel

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Slurping on non-final argument

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