I don’t know how to search this topic, then I prefer to ask.
If I did not misunderstood, the Constructor only works when all the field are supplied. I was wandering if I could define a struct and some of the fields will be generated by external functions (everything at once).
A minimal example:
mutable struct MyType
N::Integer
S::Symbol
r::Array{Float64,2}
if S == :sy1
r = foo(N)
elseif S == :sy2
r = foo2(N)
end
foo(N) = rand(N,2)
foo2(N) = rand(N,3)
end
a = MyType(10, :sy1) # do not declare r
display(a.r)
(The code above does not work, but has the main idea)
As always in Julia, you can just add methods to any function, also the constructor. It doesn’t have to be an inner constructor either:
mutable struct MyType
N::Int
S::Symbol
r::Array{Float64,2}
end
function MyType(N, S)
if S == :sy1
return MyType(N, S, rand(N, 2))
elseif S == :sy2
return MyType(N, S, rand(N, 3))
else
error("Wrong input.")
end
end
a = MyType(4, :sy2)
display(a.r)
4×3 Array{Float64,2}:
0.310291 0.371418 0.751672
0.72183 0.932101 0.00485553
0.58432 0.0196664 0.74358
0.762198 0.925545 0.776586
BTW, I changed the type of the N parameter from Integer to Int, since Integer is an abstract type, which normally leads to poor performance in structs. If you want to allow all sorts of integer types, you should make a parametric type.
Thank you DNF.
Indeed your code does what I want, but my wandering was if I could do everything at once, during the struct definition - I don’t know if this is a good idea, but I just want to know the possibility.
