`partial class` rationale

[langpavel]

Search Terms

• partial class c# google
• Partial classes  #563, Mixins, really? Why not compile-time partial class support? #14913
• When is it appropriate to use C# partial classes? (stackoverflow) — "The biggest use of partial classes is to make life easier for code generators / designers"

Suggestion

• TS already have namespace. Why it cannot have partial class only valid in namespace and in same module (like internal)?
• Partial classes may be distinct from C# implementation.
  One partial class may require declaration/implementation from another, otherwise compilation should fail.

Use Cases

• Code generation tools: ATM there is no way to extend TypeScript compiler with custom resolvers, build hooks or anything.
• Without this feature most of preconditions cannot be checked at build time and everything must be checked at boot or even worse at runtime.

Examples

• There are nice examples in the wild, VS and C# can be one well known.
• My specific use case will be to rendering GraphQL schema into partial classes, you will only implement resolvers. All checked ✔️
  (Yes. Current approaches are really bad on server.)

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[RyanCavanaugh]

You found #563 already, which has plenty of information

[langpavel]

Ok. I'm reading this as Typescript will never have partial classes

[RyanCavanaugh]

That's correct