Fixes according Cmichi's comments

examples/upgradeable-contract/upgradeable-flipper/Cargo.toml

@@ -23,13 +23,11 @@ crate-type = ["cdylib"]
 default = ["std"]
 std = [
     "ink_primitives/std",
-    "ink_metadata",
     "ink_metadata/std",
     "ink_env/std",
     "ink_storage/std",
     "ink_lang/std",
     "scale/std",
-    "scale-info",
     "scale-info/std",
 ]
 ink-as-dependency = []

examples/upgradeable-contract/upgradeable-flipper/lib.rs

@@ -15,7 +15,7 @@ pub mod flipper {
     pub struct Flipper {
         /// The field is `Upgradeable`, which means if the field is not initialized, it will be.
         ///
-        /// By default ink! throw an error that field is not initialized.
+        /// By default ink! would throw an error that the field is not initialized.
         /// With that wrapper, you can initialize the field later during the method execution,
         /// not in the constructor.
         value: Upgradeable<bool, NotInitialized>,

examples/upgradeable-contract/upgradeable-flipper/upgradeable.rs

@@ -14,11 +14,20 @@ use scale::{
     Encode,
 };
 
+/// It is a status struct for `Upgradeable`, to specify that the inner type is initialized.
 #[derive(Debug)]
 pub struct Initialized;
+/// It is a status struct for `Upgradeable`, to specify that the inner type may be not initialized and
+/// `pull_spread` should initialize it.
 #[derive(Debug)]
 pub struct NotInitialized;
 
+/// The `Upgradeable` means if the field is not initialized, it will be.
+///
+/// By default ink! would throw an error that the field is not initialized.
+/// With that wrapper, you can initialize the field later during the method execution,
+/// not in the constructor. It can be done because `SpreadLayout` for `Upgradeable<T, NotInitialized>`
+/// creates the object, if storage key is empty.
 #[derive(Debug, Decode, Encode)]
 #[cfg_attr(feature = "std", derive(scale_info::TypeInfo))]
 pub struct Upgradeable<T: PackedLayout, InitializationStatus = Initialized> {
@@ -35,6 +44,7 @@ impl<T: PackedLayout, State> Upgradeable<T, State> {
     }
 }
 
+/// It is default implementation of `SpreadLayout` for case when we don't need to init.
 impl<T: PackedLayout> SpreadLayout for Upgradeable<T, Initialized> {
     const FOOTPRINT: u64 = T::FOOTPRINT;
     const REQUIRES_DEEP_CLEAN_UP: bool = T::REQUIRES_DEEP_CLEAN_UP;
@@ -52,6 +62,7 @@ impl<T: PackedLayout> SpreadLayout for Upgradeable<T, Initialized> {
     }
 }
 
+/// It is implementation of `SpreadLayout` that initialize the inner type if it is not initialized.
 impl<T: PackedLayout + SpreadAllocate> SpreadLayout for Upgradeable<T, NotInitialized> {
     const FOOTPRINT: u64 = <T as SpreadLayout>::FOOTPRINT;
     const REQUIRES_DEEP_CLEAN_UP: bool = <T as SpreadLayout>::REQUIRES_DEEP_CLEAN_UP;
@@ -76,6 +87,8 @@ impl<T: PackedLayout + SpreadAllocate> SpreadLayout for Upgradeable<T, NotInitia
     }
 }
 
+/// Below the boilerplate code to implement `PackedLayout`, `SpreadAllocate`, `PackedAllocate`.
+
 impl<T: PackedLayout> PackedLayout for Upgradeable<T, Initialized> {
     fn pull_packed(&mut self, at: &Key) {
         <T as PackedLayout>::pull_packed(&mut self.inner, at)