Reference

JSONStyle::ToDictOption

Predefined option for JSON compatible to_dict option.

maybe of type T or nothing

TOMLStyle::ToDictOption

Predefined option for TOML compatible to_dict option.

YAMLStyle::ToDictOption

Predefined option for YAML compatible to_dict option.

ConvertNotFound

Conversion is not defined via convert_to_option. One should let the conversion fallback to Base.convert when see this.

DuplicatedFieldError(name, type)

A field with name of given option type is duplicated in the subfields option type. Thus one cannot use the field keyword convention when seeing this error.

FieldTypeConversionError(type, fieldname, fieldtype, optiontype)

A conversion from type to fieldtype belonging to fieldname in an optiontype failed.

OptionField{name}
OptionField(name::Symbol)

Trait type that denotes a field of an option type. Mainly used for dispatch purpose. name should be a Symbol.

PartialDefault{F}

Type for non-constant default value, it depends on the value of another field that has default value.

alias_map(types::Vector{Any})

Create a Dict mapping type alias to a type.

compare_options(a, b, xs...)::Bool

Compare option types check if they are the same.

convert_to_option(::Type{OptionType}, ::Type{ValueType}, x) where {OptionType, ValueType}

Convert x to type ValueType for option type OptionType. This is similar to Base.convert, but will not error if the conversion is not overloaded, and will return a ConvertNotFound object, but one can use this to avoid type piracy and define contextual conversion based on option types.

Example

One may have different string syntax for a Symbol, e.g

@option struct StringIsSymbol
    name::Symbol
end

@option struct SymbolNeedsColon
    name::Symbol
end

Configurations.convert_to_option(::Type{StringIsSymbol}, ::Type{Symbol}, x::String) = Symbol(x)

function Configurations.convert_to_option(::Type{SymbolNeedsColon}, ::Type{Symbol}, x::String)
    if startswith(x, ':')
        Symbol(x[2:end])
    else
        error("expect a Symbol, got String")
    end
end

then if we run it, we will have different behaviour by context.

julia> from_dict(StringIsSymbol, d)
StringIsSymbol(:ccc)

julia> from_dict(SymbolNeedsColon, d)
ERROR: expect a Symbol, got String

create(::Type{T}; kwargs...) where T

Create an instance of option type T from kwargs. Similar to the default keyword argument constructor, but one can use this to create custom keyword argument constructor with extra custom keywords.

field_default(::Type{T}, name::Symbol)

Return the default value of field name of an option type T.

field_defaults(::Type)

Return default values of given option types.

field_keywords(::Type{T}) where T

Return all the option type field names given T, error if there are duplicated sub-fields.

from_dict(::Type{T}, d::AbstractDict{String}; kw...) where T

Convert dictionary d to an option type T, the value of valid fields of T in this dictionary d can be override by keyword arguments.

Example

julia> @option struct OptionA
           name::String = "Sam"
           age::Int = 25
       end

julia> d = Dict{String, Any}(
           "name" => "Roger",
           "age" => 10,
       );

julia> from_dict(OptionA, d; age=25)
OptionA(;
    name = "Roger",
    age = 25,
)

from_dict(::Type{OptionType}, ::OptionField{f_name}, ::Type{T}, x) where {OptionType, f_name, T}

For option type OptionType, convert the object x to the field type T and assign it to the field f_name. Raise FieldTypeConversionErrors errors if Base.convert raises exception

ERROR: MethodError: Cannot `convert` an object of type ...

from_dict_generated(::Type{OptionType}, value::Symbol) where {OptionType}

Generate a specialized Julia expression to convert an AbstractDict{String} to our OptionType.

from_dict_specialize(::Type{OptionType}, x) where {OptionType}

A specialized from_dict method for option type OptionType. This is usually generated by @option, but one may also specialized this manually to acheive maximal performance.

from_field_kwargs(::Type{T}; kw...) where T

Convert keyword arguments to given option type T using the field keyword convention.

from_kwargs!(d::AbstractDict{String}, ::Type{T}, prefix::Maybe{Symbol} = nothing; kw...) where T

Internal method for inserting keyword arguments to given dictionary object d. It will overwrite existing keys in d if it is specified by keyword argument.

from_kwargs(::Type{T}; kw...) where T

Convert keyword arguments to given option type T using the underscore convention.

from_kwargs(convention!, ::Type{T}; kw...) where T

Convert keyword arguments to given option type T using convention!. See also from_dict.

Convention

• from_underscore_kwargs!: use _ to disambiguate subfields of the same name, this is the default behaviour.
• from_field_kwargs!: do not disambiguate subfields, errors if there are disambiguity

from_toml(::Type{T}, filename::String; kw...) where T

Convert a given TOML file filename to an option type T. Valid fields can be override by keyword arguments. See also from_dict.

from_toml_if_exists(::Type{T}, filename::String; kw...) where T

Similar to from_toml but will create the option instance via from_kwargs(T;kw...) instead of error if the file does not exist.

from_underscore_kwargs(::Type{T}; kw...) where T

Convert keyword arguments to given option type T using the underscore convention.

has_same_reflect_field(types::Vector{Any})

Check if all types has the same reflect field name.

ignore_extra(option_type) -> Bool

Return true if the option type ignores extra fields when read from a dict-like object.

Example

julia> Configurations.ignore_extra(::Type{MyOption}) = true

is_option(x)

Check if x is an option type or not.

is_option_maybe(::Type{T}) where T

T is an option struct or if T is an union, one of the types is an option struct.

to_dict(x, option::ToDictOption) -> OrderedDict

Convert an object x to an OrderedDict with ToDictOption specified.

Example

to_dict(x, TOMLStyle) # TOML compatible
to_dict(x, YAMLStyle) # YAML compatible
to_dict(x, JSONStyle) # JSON compatible

to_dict(x; include_defaults=true, exclude_nothing=false) -> OrderedDict

Convert an object x to an OrderedDict.

Kwargs

• include_defaults: include the default value, default is true.
• exclude_nothing: exclude fields that have value nothing, this supersedes include_defaults when they are both true.

Format Compatibilty

When mapping an option struct from Julia to TOML/YAML/JSON/etc. format, there are some subtle semantic compatibilty one need to deal with, we provide some convenient predefined conversion option constants as TOMLStyle, YAMLStyle, JSONStyle.

to_toml([f::Function], io::IO, option; sorted=false, by=identity, kw...)

Convert an instance option of option type to TOML and write it to IO. See to_dict for other valid keyword options. See also TOML.print in the stdlib for the explaination of sorted, by and f.

Exclude nothing

In TOML specification, there is no null type. One should exclude the field if it is not specified (of value nothing in Julia). In to_toml the option exclude_nothing is always true.

In most cases, nothing is used with another type to denote optional or not specified field, thus one should always put a default value nothing to the option struct, e.g

One should define

@option struct OptionX
    a::Union{Nothing, Int} = nothing
    b::Maybe{Int} = nothing
end

Here Maybe{T} is a convenient alias of Union{Nothing, T}.

to_toml([f::Function], filename::String, option; sorted=false, by=identity, kw...)

Convert an instance option of option type to TOML and write it to filename. See also TOML.print.

to_toml(x; sorted=false, by=identity, kw...)

Convert an instance x of option type to TOML and write it to String. See also TOML.print.

to_toml does not export fields that are of the same values as the defaults. This can be overridden by changing include_defaults to true.

type_alias(::Type{OptionType}) -> String

Return the alias name of given OptionType.

underscore_keywords(::Type{T}) where T

Return keywords given T using the underscore convention.

@option [alias::String] <struct def>

Define an option struct type. This will auto-generate methods that parse a given Dict{String} object (the keys must be of type String) into an instance of the struct type you defined. One can use alias string to distinguish multiple possible option type for the same field.

Special Types

• Maybe{T}: this type is equivalent to Union{Nothing, T} and is treated specially in @option, it will always have a default value of nothing if not specified.
• Reflect: this type is treated specially to allow one to use a field to store the corresponding type information.

Example

One can define option type via @option macro with or without an alias.

julia> "Option A"
       @option "option_a" struct OptionA
           name::String
           int::Int = 1
       end

julia> "Option B"
       @option "option_b" struct OptionB
           opt::OptionA = OptionA(;name = "Sam")
           float::Float64 = 0.3
       end
julia> option = from_dict(OptionB, d)
OptionB(;
    opt = OptionA(;
        name = "Roger",
        int = 2,
    ),
    float = 0.33,
)

when there are multiple possible option type for one field, one can use the alias to distinguish them

julia> @option struct OptionD
           opt::Union{OptionA, OptionB}
       end

julia> d1 = Dict{String, Any}(
               "opt" => Dict{String, Any}(
                   "option_b" => d
               )
           );

julia> from_dict(OptionD, d1)
OptionD(;
    opt = OptionB(;
        opt = OptionA(;
            name = "Roger",
            int = 2,
        ),
        float = 0.33,
    ),
)

@type_alias <type> <name::String>

Define a type alias for option type type. The corresponding type must be a concrete type in order to map this Julia type to a human readable markup language (e.g TOML, YAML, etc.).