Structs in Julia

Immutable by default; mutable is a separate promise.

# Structs are immutable by default; mutable opts in per type.
struct Target
    name::String
    magnitude::Float64
end

mutable struct DomeState
    open::Bool
    azimuth::Int
end

vega = Target("Vega", 0.03)
println("$(vega.name) at magnitude $(vega.magnitude)")

dome = DomeState(false, 0)
dome.open = true
dome.azimuth = 245
println("Dome open at $(dome.azimuth) degrees")

How it works

struct Target fields are fixed once constructed.
mutable struct DomeState opts into assignment.
Construction is positional: Target("Vega", 0.03).

Keywords and builtins used here

Bool
DomeState
Float64
Int
String
Target
end
false
mutable
struct
true

The run, in numbers

Lines: 18
Characters to type: 361
Tokens: 79
Three-star pace: 70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 68 seconds.

Type this snippet

Step 1 of 3 in Types, step 16 of 27 in Language basics.

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Structs in other languages