DefineSingletons

Define singleton and it's pretty-printing show in one go:

julia> using DefineSingletons

julia> @def_singleton mysingleton;

julia> mysingleton
mysingleton

julia> Base.issingletontype(typeof(mysingleton))
true

See more in the docstring of @def_singleton.

@def_singleton singleton_name
@def_singleton singleton_name::SingletonType
@def_singleton singleton_name::SingletonType <: SuperType
@def_singleton singleton_name isa SuperType
@def_singleton singleton_name = SingletonType()

Define a singleton named singleton_name and its two-argument show(::IO, ::SingletonType) method.

With the form singleton_name = SingletonType(), the type SingletonType can be a parametric type as long as Base.issingletontype(SingletonType) is true.

Examples

julia> using DefineSingletons

julia> @def_singleton mysingleton::MySingletonType;

julia> mysingleton
mysingleton

julia> mysingleton isa MySingletonType
true

julia> mysingleton === MySingletonType()
true

With supertype:

julia> abstract type MySuperType end;

julia> @def_singleton mysingleton2::MySingletonType2 <: MySuperType;

julia> mysingleton2
mysingleton2

julia> mysingleton2 isa MySingletonType2
true

julia> MySingletonType2 <: MySuperType
true

julia> @def_singleton mysingleton3 isa MySuperType;

julia> mysingleton3 isa MySuperType
true

With pre-existing parametric type:

julia> struct MyParametricType{T} end;

julia> @def_singleton P1 = MyParametricType{1}();

julia> P1
P1

julia> P1 isa MyParametricType{1}
true