Improve inferrability and use enums rather than types for some settings

Project.toml

@@ -12,7 +12,7 @@ Observables = "510215fc-4207-5dde-b226-833fc4488ee2"
 [compat]
 GeometryBasics = "0.4.1"
 Match = "^1"
-Observables = "0.3, 0.4"
+Observables = "0.4"
 julia = "1"
 
 [extras]

src/GridLayoutBase.jl

@@ -1,11 +1,15 @@
 module GridLayoutBase
 
+if isdefined(Base, :Experimental) && isdefined(Base.Experimental, Symbol("@compiler_options"))
+ @eval Base.Experimental.@compiler_options compile=min optimize=1
+end
+
 using GeometryBasics
 using Observables
 using Match
 
-const DEFAULT_COLGAP = Ref{Any}(20.0)
-const DEFAULT_ROWGAP = Ref{Any}(20.0)
+const DEFAULT_COLGAP = Ref{Float64}(20.0)
+const DEFAULT_ROWGAP = Ref{Float64}(20.0)
 # These function refs can be mutated by other packages to override the default
 # way of retrieving default column and row gap sizes
 const DEFAULT_ROWGAP_GETTER = Ref{Function}(() -> DEFAULT_ROWGAP[])

src/geometry_integration.jl

@@ -7,12 +7,13 @@ width(rect::Rect{2}) = right(rect) - left(rect)
 height(rect::Rect{2}) = top(rect) - bottom(rect)
 
 
-function BBox(left::Number, right::Number, bottom::Number, top::Number)
+function BBox(left::Float32, right::Float32, bottom::Float32, top::Float32)
  mini = (left, bottom)
  maxi = (right, top)
  return Rect2f(mini, maxi .- mini)
 end
-
+BBox(left::Number, right::Number, bottom::Number, top::Number) =
+ BBox(Float32(left)::Float32, Float32(right)::Float32, Float32(bottom)::Float32, Float32(top)::Float32)
 
 function RowCols(ncols::Int, nrows::Int)
  return RowCols(
@@ -23,17 +24,17 @@ function RowCols(ncols::Int, nrows::Int)
  )
 end
 
-Base.getindex(rowcols::RowCols, ::Left) = rowcols.lefts
-Base.getindex(rowcols::RowCols, ::Right) = rowcols.rights
-Base.getindex(rowcols::RowCols, ::Top) = rowcols.tops
-Base.getindex(rowcols::RowCols, ::Bottom) = rowcols.bottoms
+Base.getindex(rowcols::RowCols, side::Side) = side == Left ? rowcols.lefts :
+ side == Right ? rowcols.rights :
+ side == Top ? rowcols.tops :
+ side == Bottom ? rowcols.bottoms : throw_side(side)
 
 """
  eachside(f)
 Calls f over all sides (Left, Right, Top, Bottom), and creates a BBox from the result of f(side)
 """
 function eachside(f)
-    return BBox(f(Left()), f(Right()), f(Bottom()), f(Top()))
+    return BBox(f(Left), f(Right), f(Bottom), f(Top))
 end
 
 """