onflow/cadence v0.20.0 on GitHub

This release culminates a half-year effort to improve the Cadence storage layer, i.e. how Cadence values are stored in accounts, in particular arrays, dictionaries, and composite values. @fxamacker and @ramtinms designed and implemented completely new array and ordered map data structures, resulting in atree. These data structures are fast and scalable: they allow efficient access and allow efficient modifications to arrays and dictionaries with very large number of elements. @turbolent and @SupunS integrated this new library into Cadence. This new storage layer also fixed a bug in the resource owner field. Please see the breaking changes section for more details.

In addition, this release saw several feature and documentation contributions by new community members. Thank you!

💥 Breaking Changes

With the storage layer update, the owner field of resources is now implemented correctly, as originally designed:
The field is only non-nil if the resource is currently in storage, and is always nil if the resource is on the stack.
This breaking change is actually a bug fix, as the owner field was previously implemented incorrectly: After a resource was moved out of storage onto the stack, the owner field was still referring to the account the resource was stored in.
Please ensure your Cadence programs do not rely on the broken behaviour and update them if needed.
For example, in a function that is passed a resource as an argument, the resource's owner field will always be nil:
```
pub fun deposit(token: @NonFungibleToken.NFT) {
    // token.owner is always nil!
    // ...
}
```
Add limit on call stack depth (#1138) @SupunS

⭐ Features

Add Path.toString() with tests and documentation. (#1141) @rheaplex
Adding toLower() to String type (#1176) @bjartek
Add isSubtype function for runtime values (#1189) @dsainati1

🛠 Improvements

Introduce TokenStream interface (#1113) @jsatdapr
Remove obsolete script/transaction parameter check (#1114) @SupunS
Add static type to host functions (#1144) @SupunS
Infer RHS of nil-coalescing operator to have non-optional type of LHS (#1154) @turbolent
Use new atree library for arrays, dictionaries, and composite values (#1156) @turbolent
Limit error line lengths (#1165) @turbolent
Add dynamic sub-typing for function types (#1172) @SupunS
Remove CompositeDeclarations check from FunctionEntryPointDeclaration (#1175) @janezpodhostnik
Check slab and account storage health (#1193) @turbolent

🐞 Bug Fixes

Fix export errors by properly wrapping in runtime errors (#1139) @SupunS
Fix array function member type creation (#1146) @SupunS
Add missing function type for Path.toString (#1150) @turbolent
Consider constant-sized type's size when checking dynamic array type (#1158) @turbolent
Fix move operator on empty resource collections (#1159) @SupunS
Fix block ID static type (#1168) @turbolent
Reintroduce and fix stringAtreeValue (#1174) @turbolent
Fix reference uses after moves (#1180) @turbolent

📖 Documentation

Core events documentation (#1110) @sideninja
Migrate remaining docs from docs site. (#1155) @10thfloor
Fix bad link in Cadence tutorial page 01 (#1167) @kerrywei
Fixing typo (#1182) @sovietspy2
Fix units on storageUsed and storageCapacity data members (bytes) (#1184) @Giners
Fix typos (#1187, #1188, #1191, #1194) @markstrefford

🙌 New Contributors

Thank you to all new contributors:

Changelog

v0.19.1...v0.20.0