IsDef.jl

This package provides primitives for dispatching on whether certain methods are implemented or not.

For installation or usage, open julia repl and run

using IsDef

which gives you access to following functions

• isdef(f, arg1, arg2)::Bool / isdef(f, Arg1Type, Arg2Type)::Bool checks whether a function is defined for the given types.

  If at least one of the arguments is not a type, all arguments are automatically converted to types for you.

• Out(f, arg1, arg2)::ReturnType / Out(f, Arg1Type, Arg2Type)::ReturnType returns the returntype of the given functioncall.

  Note, that Out may return an abstract type that is wider than necessary, like e.g. Any. If a functioncall is not defined, or predictably throws an error, IsDef.NotApplicable is returned. Out is internally used by isdef.

Internally of Out(f, Arg1Type, Arg2Type) a one-argument-version of Out is used which expects a single Tuple type, specifying the entire call signature. This is the heart of the IsDef package. For the example it would be

• Out(Tuple{typeof(f), Arg1Type, Arg2Type})

If you want to specify inference of your method (output of Out), or whether it is defined (output of isdef), you need to overload this very one-argument method of Out. For the example it could be

• Out(::Type{<:Tuple{typeof(f), Arg1Type, Arg2Type, Vararg}}) = ReturnType

Enjoy maintainable type inference.