Add option for lazy cache

Author: blegat

src/instantiate.jl

@@ -124,6 +124,8 @@ function _instantiate_and_check(optimizer_constructor::OptimizerWithAttributes)
     return optimizer
 end
 
+struct IfIncrementalInterfaceNotSupported{T} end
+
 """
     instantiate(
         optimizer_constructor,
@@ -163,6 +165,7 @@ function instantiate(
     (@nospecialize optimizer_constructor);
     with_bridge_type::Union{Nothing,Type} = nothing,
     with_cache_type::Union{Nothing,Type} = nothing,
+    cache_only_if_incremental_interface_not_supported = false,
 )
     if with_bridge_type !== nothing && with_cache_type !== nothing
         if with_bridge_type != with_cache_type
@@ -175,20 +178,19 @@ function instantiate(
         end
     end
     optimizer = _instantiate_and_check(optimizer_constructor)
-    if with_bridge_type === nothing
-        if with_cache_type === nothing
-            return optimizer
-        end
+    if !isnothing(with_bridge_type) && isnothing(with_cache_type)
+        with_cache_type = T
+        cache_only_if_incremental_interface_not_supported = true
+    end
+    if cache_only_if_incremental_interface_not_supported && !supports_incremental_interface(optimizer)
+        with_cache_type = nothing
         cache = default_cache(optimizer, with_cache_type)
-        return Utilities.CachingOptimizer(cache, optimizer)
-    else
-        if with_cache_type !== nothing ||
-           !supports_incremental_interface(optimizer)
-            cache = default_cache(optimizer, with_bridge_type)
-            optimizer = Utilities.CachingOptimizer(cache, optimizer)
-        end
-        return Bridges.full_bridge_optimizer(optimizer, with_bridge_type)
+        optimizer = Utilities.CachingOptimizer(cache, optimizer)
+    end
+    if !isnothing(with_bridge_type)
+        optimizer = Bridges.full_bridge_optimizer(optimizer, with_bridge_type)
     end
+    return optimizer
 end
 
 """