This is a package I use to handle numerical-model parameters, thus the name. However, it should be useful otherwise too. It has two main features:
Checkout my ten minute JuliaCon 2018 talk.
@with_kw which decorates a type definition to
allow default values and a keyword constructor:
julia> using Parameters julia> @with_kw struct A a::Int = 6 b::Float64 = -1.1 c::UInt8 end julia> A(c=4) A a: 6 b: -1.1 c: 4 julia> A() ERROR: Field 'c' has no default, supply it with keyword. julia> A(c=4, a = 2) A a: 2 b: -1.1 c: 4
The macro also supports constructors for named tuples with default values; e.g.
julia> MyNT = @with_kw (x = 1, y = "foo", z = :(bar)) (::#5) (generic function with 2 methods) julia> MyNT() (x = 1, y = "foo", z = :bar) julia> MyNT(x = 2) (x = 2, y = "foo", z = :bar)
v0.6 users: since
NamedTuplesare not supported in base Julia v0.6, you must import the
NamedTuples.jlpackage. Be aware of this issue with keyword arguments in v0.6.
Unpacking is done with
@pack! is similar):
struct B a b c end @unpack a, c = B(4,5,6) # is equivalent to BB = B(4,5,6) a = BB.a c = BB.c
The features are:
*is the type name.
@unpack(work with any types).
The keyword-constructor and default-values functionality will probably make it into Julia (# 10146, #533 and #6122) although probably not with all the features present in this package. I suspect that this package should stay usable & useful even after this change lands in Julia. Note that keyword functions are currently slow in Julia, so these constructors should not be used in hot inner loops. However, the normal positional constructor is also provided and could be used in performance critical code.
NEWS.md keeps tabs on updates.
Implementing similar things:
Base.@kwdefhas functionality similar to
@with_kwbut more limited. However, with Julia v1.1 its capabilities will be much enhanced, see #29316. If that is enough, ditch the Parameters.jl dependency.
3 days ago