mark some fields that should not be changed as const

Project.toml

@@ -1,7 +1,10 @@
 name = "DiscretePIDs"
 uuid = "c1363496-6848-4723-8758-079b737f6baf"
 authors = ["Fredrik Bagge Carlson"]
-version = "0.1.3"
+version = "0.1.4"
+
+[deps]
+Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 
 [compat]
 julia = "1.7"

src/DiscretePIDs.jl

@@ -2,6 +2,8 @@ module DiscretePIDs
 
 export DiscretePID, calculate_control!, set_K!, set_Td!, set_Ti!
 
+using Printf
+
 """
     DiscretePID{T}
 """
@@ -15,17 +17,17 @@ mutable struct DiscretePID{T} <: Function
     "Reset time"
     Tt::T 
     "Maximum derivative gain"
-    N::T 
+    const N::T 
     "Fraction of set point in prop. term"
     b::T 
     "Low output limit"
     umin::T 
     "High output limit"
     umax::T 
     "Sampling period"
-    Ts::T 
+    const Ts::T 
     bi::T
-    ar::T
+    const ar::T
     bd::T
     ad::T
     "Integral state"
@@ -78,8 +80,8 @@ function DiscretePID(;
     Tt = Ti > 0 && Td > 0 ? typeof(K)(√(Ti*Td)) : typeof(K)(10),
     N  = typeof(K)(10),
     b  = typeof(K)(1),
-    umin = typemin(K),
-    umax = typemax(K),
+    umin = typemin(typeof(K)),
+    umax = typemax(typeof(K)),
     Ts,
     I    = zero(typeof(K)),
     D    = zero(typeof(K)),
@@ -175,10 +177,11 @@ end
 (pid::DiscretePID)(args...) = calculate_control!(pid, args...)
 
 function Base.show(io::IO, ::MIME"text/plain", pid::DiscretePID)
-    println(io, "$(typeof(pid)) with parameters and state:")
+    println(io, "$(typeof(pid))( # with parameters and state:")
     for name in fieldnames(DiscretePID)
-        println(io, name, ":\t", getfield(pid, name))
+        @printf(io, "    %-14.7g,# %s\n", getfield(pid, name), name)
     end
+    println(io, ")")
 end