Apply suggestions from code review

Co-authored-by: Mateusz Baran <[email protected]>

src/plans/stopping_criterion.jl

@@ -248,7 +248,7 @@ default. You can also provide an inverse_retraction_method for the `distance` or
 to use its default inverse retraction.
 """
 mutable struct StopWhenChangeLess{
-    F,IRT<:AbstractInverseRetractionMethod,TSSA<:StoreStateAction,N
+    F,IRT<:AbstractInverseRetractionMethod,TSSA<:StoreStateAction,N<:Union{Missing,Real}
 } <: StoppingCriterion
     threshold::F
     last_change::F
@@ -263,7 +263,7 @@ function StopWhenChangeLess(
     storage::StoreStateAction=StoreStateAction(M; store_points=Tuple{:Iterate}),
     inverse_retraction_method::IRT=default_inverse_retraction_method(M),
     outer_norm::N=missing,
-) where {F,N,IRT<:AbstractInverseRetractionMethod}
+) where {F,N<:Union{Missing,Real},IRT<:AbstractInverseRetractionMethod}
     return StopWhenChangeLess{F,IRT,typeof(storage),N}(
         ε, zero(ε), storage, inverse_retraction_method, -1, outer_norm
     )
@@ -278,7 +278,7 @@ function (c::StopWhenChangeLess)(mp::AbstractManoptProblem, s::AbstractManoptSol
     if has_storage(c.storage, PointStorageKey(:Iterate))
         M = get_manifold(mp)
         p_old = get_storage(c.storage, PointStorageKey(:Iterate))
-        r = (has_components(M) && !ismissing(c.outer_norm)) ? [c.outer_norm] : []
+        r = (has_components(M) && !ismissing(c.outer_norm)) ? (c.outer_norm,) : ()
         c.last_change = distance(
             M, get_iterate(s), p_old, c.inverse_retraction_method, r...
         )
@@ -513,7 +513,7 @@ indicates to stop when [`get_gradient`](@ref) is in (norm of) its change less th
 `vector_transport_method` denotes the vector transport ``$(_tex(:Cal,"T"))`` used.
 """
 mutable struct StopWhenGradientChangeLess{
-    F,VTM<:AbstractVectorTransportMethod,TSSA<:StoreStateAction,N
+    F,VTM<:AbstractVectorTransportMethod,TSSA<:StoreStateAction,N<:Union{Missing,Real}
 } <: StoppingCriterion
     threshold::F
     last_change::F
@@ -530,7 +530,7 @@ function StopWhenGradientChangeLess(
     ),
     vector_transport_method::VTM=default_vector_transport_method(M),
     outer_norm::N=missing,
-) where {F,N,VTM<:AbstractVectorTransportMethod}
+) where {F,N<:Union{Missing,Real},VTM<:AbstractVectorTransportMethod}
     return StopWhenGradientChangeLess{F,VTM,typeof(storage),N}(
         ε, zero(ε), storage, vector_transport_method, -1, outer_norm
     )
@@ -554,7 +554,7 @@ function (c::StopWhenGradientChangeLess)(
         X_old = get_storage(c.storage, VectorStorageKey(:Gradient))
         p = get_iterate(s)
         Xt = vector_transport_to(M, p_old, X_old, p, c.vector_transport_method)
-        r = (has_components(M) && !ismissing(c.outer_norm)) ? [c.outer_norm] : []
+        r = (has_components(M) && !ismissing(c.outer_norm)) ? (c.outer_norm,) : ()
         c.last_change = norm(M, p, Xt - get_gradient(s), r...)
         if c.last_change < c.threshold && k > 0
             c.at_iteration = k
@@ -625,7 +625,7 @@ $(_tex(:norm, "X"; index="p")) = $(_tex(:Bigl))( $(_tex(:sum))_{k=1}^n $(_tex(:n
 ```
 
 where the sum turns into a maximum for the case ``r=∞``.
-The `outer_norm` has no effect on manifols, that do not consist of components.
+The `outer_norm` has no effect on manifolds that do not consist of components.
 
 If you pass in your individual norm, this can be deactivated on such manifolds
 by passing `missing` to `outer_norm`.
@@ -638,15 +638,15 @@ Create a stopping criterion with threshold `ε` for the gradient, that is, this
 indicates to stop when [`get_gradient`](@ref) returns a gradient vector of norm less than `ε`,
 where the norm to use can be specified in the `norm=` keyword.
 """
-mutable struct StopWhenGradientNormLess{F,TF,N} <: StoppingCriterion
+mutable struct StopWhenGradientNormLess{F,TF,N<:Union{Missing,Real}} <: StoppingCriterion
     norm::F
     threshold::TF
     last_change::TF
     at_iteration::Int
     outer_norm::N
     function StopWhenGradientNormLess(
         ε::TF; norm::F=norm, outer_norm::N=missing
-    ) where {F,TF,N}
+    ) where {F,TF,N<:Union{Missing,Real}}
         return new{F,TF,N}(norm, ε, zero(ε), -1, outer_norm)
     end
 end
@@ -659,7 +659,7 @@ function (sc::StopWhenGradientNormLess)(
         sc.at_iteration = -1
     end
     if (k > 0)
-        r = (has_components(M) && !ismissing(sc.outer_norm)) ? [sc.outer_norm] : []
+        r = (has_components(M) && !ismissing(sc.outer_norm)) ? (sc.outer_norm,) : ()
         sc.last_change = sc.norm(M, get_iterate(s), get_gradient(s), r...)
         if sc.last_change < sc.threshold
             sc.at_iteration = k