How to get the type metadata for a field?

[Azoy]

Cross posting https://github.com/Azoy/Echo/discussions/24#discussioncomment-622378

NSExceptional asks:

How does one get the type metadata for a field? I see this in FieldType.swift…

// This isn't used anywhere yet... ?
struct FieldType {

So far all I can see is a way to get the type name of a field, but I don't know how to turn that into a real Type without scanning the binary in memory

[Azoy]

Cross posting answer: https://github.com/Azoy/Echo/discussions/24#discussioncomment-622404

Azoy answers:

Documentation states it here: https://github.com/Azoy/Echo/wiki/FieldRecord#mangledtypename , but it seems the wiki generator didn't create the code comment for this example. Here:

let metadata = reflect(SomeType.self) as! TypeMetadata
for field in metadata.contextDescriptor.fields.records {
  guard field.hasMangledTypeName else { continue }

  let fieldType = metadata.type(of: field.mangledTypeName)
}

Keep in mind that we need to demangle this type name, so doing this can be expensive, but I do having caching for this mangled name in place to help speed up subsequent demangling on the same field for the same metadata.

[Azoy]

Cross posting reply: https://github.com/Azoy/Echo/discussions/24#discussioncomment-622416

NSExceptional replies:

I just found this snippet in FieldDescriptor.swift and was about to answer my own Q with it! Thanks :)

/// The mangled type name that demangles to the field's type.
///
/// Note: Use this in combination with metadata's type(of:) method to get a
///       field's type.
///
/// Example:
///     let metadata = reflect(SomeType.self) as! TypeMetadata
///     for field in metadata.contextDescriptor.fields.records {
///       let fieldType = metadata.type(of: field.mangledTypeName)
///     }
public var mangledTypeName: UnsafeRawPointer