Automatically add a constructor for building objects with Dict and JSON String to DataType

You can use macro @add_init before struct definition. Then get a constructor initialized by JSON string or Dict. Of course, you can also use @add_jsoninit or @add_dictinit to separately add JSON or Dict constructor.

using AddInit

@add_init struct Test
    field::AbstractString
end

Test("{"field":"a"}") == Test("a")  # true
Test(Dict("field"=>"a")) == Test("a")  #true

It can also cooperate with Base.@kwdef use.

@Base.kwdef struct Test
    a::Int
    b::Int=2
    c::Int
end
@add_init Test

Test(Dict("a"=>1, "c"=>3)) == Test(1,2,3)   # true

Of course, it also applies to nested objects

@add_init struct A
    v::Int
end 
@add_init struct B
    a::A
end
 
B(Dict("a"=>Dict("v"=>1))) == B(A(1))  # true

1. Do not use this macro when a single attribute type is String or Dict, which will cause ambiguity.
2. It's best not to use abstract types for type annotation unless you need to assign the original value directly.