## Type-stable DollarAdjust with typed zero (#1026)

* refactor: make DollarAdjust parametric for type stability

- Convert DollarAdjust to parametric type DollarAdjust{T<:Real}
- Add type parameters to function signatures using DollarAdjust
- Replace literal 0.0 returns with zero(T) for type stability
- Add eltype method for DollarAdjust type inference

* fix: update DollarAdjust type parameter for cost calculation function

Author: mgyoo86

src/actors/costing/aries_costing_actor.jl

@@ -259,10 +259,10 @@ end
 
 Capital cost for each layer in the build
 """
-function cost_direct_capital_ARIES(layer::IMAS.build__layer, cst::IMAS.costing, da::DollarAdjust)
+function cost_direct_capital_ARIES(layer::IMAS.build__layer, cst::IMAS.costing, da::DollarAdjust{T}) where {T<:Real}
     da.year_assessed = 2016
     if layer.type == Int(_oh_)
-        return 0.0 # oh is part of the pf_active calculation
+        return zero(T) # oh is part of the pf_active calculation
     elseif layer.type == Int(_tf_)
         build = IMAS.parent(IMAS.parent(layer))
         cost = layer.volume * (unit_cost(build.tf.technology, cst) * (1.0 - build.tf.nose_hfs_fraction) .+ unit_cost(Material(:steel), cst) * build.tf.nose_hfs_fraction)
@@ -452,14 +452,14 @@ end
 
 NOTE: ARIES https://cer.ucsd.edu/_files/publications/UCSD-CER-13-01.pdf
 """
-function cost_direct_capital_ARIES(::Val{:balance_of_plant_equipment}, power_thermal::Real, power_electric_generated::Real, da::DollarAdjust, dd::IMAS.dd)
+function cost_direct_capital_ARIES(::Val{:balance_of_plant_equipment}, power_thermal::Real, power_electric_generated::Real, da::DollarAdjust{T}, dd::IMAS.dd) where {T<:Real}
     da.year_assessed = 2009
     power_thermal = power_thermal / 1E6
     power_electric_generated = power_electric_generated / 1E6
     bop = dd.balance_of_plant
 
     if power_thermal <= 0.0
-        return 0.0
+        return zero(T)
     else
         if contains(lowercase(bop.power_plant.power_cycle_type), "rankine")
             cost = 350.0 * (power_thermal / 2620.0)^0.7 # Turbine equipment

src/actors/costing/costing_utils.jl

@@ -48,16 +48,17 @@ end
 #= ==================== =#
 #  Inflation Adjustment  #
 #= ==================== =#
-mutable struct DollarAdjust
-    future_inflation_rate::Real
-    construction_start_year::Real
+mutable struct DollarAdjust{T<:Real}
+    future_inflation_rate::T
+    construction_start_year::T
     year_assessed::Union{Missing,Int}
     year::Union{Missing,Int}
 end
 
-function DollarAdjust(dd::IMAS.dd)
-    return DollarAdjust(dd.costing.future.inflation_rate, dd.costing.construction_start_year, missing, missing)
+function DollarAdjust(dd::IMAS.dd{T}) where {T<:Real}
+    return DollarAdjust{T}(dd.costing.future.inflation_rate, dd.costing.construction_start_year, missing, missing)
 end
+Base.eltype(::Type{DollarAdjust{T}}) where {T} = T
 
 """
     load_inflation_rate()
@@ -95,10 +96,10 @@ end
 
 Adjusts costs assessed in a previous year to current or future dollar amount
 """
-function future_dollars(dollars::Real, da::DollarAdjust)
+function future_dollars(dollars::Real, da::DollarAdjust{T})::T where {T<:Real} 
 
     if dollars == 0.0
-        return 0.0
+        return zero(T)
     end
 
     CPI = load_inflation_rate()
@@ -129,7 +130,7 @@ function future_dollars(dollars::Real, da::DollarAdjust)
     # wipe out year_assessed each time to force developer to enter of `da.year_assessed` and avoid using the wrong year 
     da.year_assessed = missing
 
-    return value
+    return T(value)
 end
 
 #= ================== =#

src/actors/costing/sheffield_costing_actor.jl

@@ -347,13 +347,13 @@ function cost_direct_capital_Sheffield(::Val{:buildings}, bd::IMAS.build, da::Do
     return future_dollars(cost, da)
 end
 
-function cost_direct_capital_Sheffield(::Val{:blanket}, cap::Bool, dd::IMAS.dd, da::DollarAdjust)
+function cost_direct_capital_Sheffield(::Val{:blanket}, cap::Bool, dd::IMAS.dd, da::DollarAdjust{T}) where {T<:Real}
     da.year_assessed = 2016
 
     cost = 0.0
 
     if cap == false
-        return 0.0
+        return zero(T)
     else
         bd = dd.build
         cst = dd.costing