Parsing to custom types

If you specify an arg_type setting (see the Argument entry settings section) for an option or an argument, parse_args will try to parse it, i.e. to convert the string to the specified type. For Number types, Julia's built-in parse function will be used. For other types, first convert and then the type's constructor will be tried. In order to extend this functionality, e.g. to user-defined custom types, without adding methods to convert or the constructor, you can overload the ArgParse.parse_item function. Example:

struct CustomType

function ArgParse.parse_item(::Type{CustomType}, x::AbstractString)
    return CustomType(parse(Int, x))

Note that the second argument needs to be of type AbstractString to avoid ambiguity errors. Also note that if your type is parametric (e.g. CustomType{T}), you need to overload the function like this: function ArgParse.parse_item(::Type{CustomType{T}}, x::AbstractString) where {T}.