ResultTypes

ResultTypes provides a Result type which can hold either a value or an error. This allows us to return a value or an error in a type-stable manner without throwing an exception.

Usage

Basic

We can construct a Result that holds a value:

julia> x = Result(2); typeof(x)
ResultTypes.Result{Int64,Exception}

or a Result that holds an error:

julia> x = ErrorResult(Int, "Oh noes!"); typeof(x)
ResultTypes.Result{Int64,ErrorException}

or either with a different error type:

julia> x = Result(2, DivideError); typeof(x)
ResultTypes.Result{Int64,DivideError}

julia> x = ErrorResult(Int, DivideError()); typeof(x)
ResultTypes.Result{Int64,DivideError}

Exploiting Function Return Types

We can take advantage of automatic conversions in function returns (a Julia 0.5 feature):

julia> function integer_division(x::Int, y::Int)::Result{Int, DivideError}
           if y == 0
               return DivideError()
           else
               return div(x, y)
           end
       end
integer_division (generic function with 1 method)

This allows us to write code in the body of the function that returns either a value or an error without manually constructing Result types.

julia> integer_division(3, 4)
Result(0)

julia> integer_division(3, 0)
ErrorResult(Int64, DivideError())