New Issue: [Feature Request]: add 'Reflection.getField' on a type to return the type

jabraham17 · April 1, 2026, 4:42pm

28629, "jabraham17", "[Feature Request]: add 'Reflection.getField' on a type to return the type", "2026-04-01T16:40:59Z"

github.com/chapel-lang/chapel

[Feature Request]: add `Reflection.getField` on a type to return the type

opened 04:40PM - 01 Apr 26 UTC

jabraham17

area: Libraries / Modules type: Feature Request

While implementing improved unions and working closely with the reflection modul…e, I noticed this asymmetry. I can do `getField(myObj, index)`, but not `getField(MyType, i)`. However, the underlying primitive supports this and we have tests that rely on that pattern For example ```chapel proc type deserializeFrom(reader: fileReader(?), ref deserializer) { type fieldType = __primitive("field by num", this, 0); return new G(reader.read(fieldType)); } ``` In this case, `this` is a type. In order to determine the field type without the primitive, you need a dummy variable ```chapel proc type deserializeFrom(reader: fileReader(?), ref deserializer) { var dummy: this; type fieldType = Reflection.getField(dummy, 0).type; return new G(reader.read(fieldType)); } ``` This feels very unsatisfying. I could imagine a pair of functions like these, which when given a type just always return the type of the field ```chapel proc getField(type MyType, param idx: int) type proc getField(type MyType, param name: string) type ``` I could see how it these functions could be confusing, and perhaps the name should be `getFieldType`. But I do think this is useful functionality to include in the Reflection module.

While implementing improved unions and working closely with the reflection module, I noticed this asymmetry. I can do getField(myObj, index), but not getField(MyType, i). However, the underlying primitive supports this and we have tests that rely on that pattern

For example

  proc type deserializeFrom(reader: fileReader(?), ref deserializer) {
    type fieldType = __primitive("field by num", this, 0);
    return new G(reader.read(fieldType));
  }

In this case, this is a type. In order to determine the field type without the primitive, you need a dummy variable

  proc type deserializeFrom(reader: fileReader(?), ref deserializer) {
    var dummy: this;
    type fieldType = Reflection.getField(dummy, 0).type;
    return new G(reader.read(fieldType));
  }

This feels very unsatisfying.

I could imagine a pair of functions like these, which when given a type just always return the type of the field

proc getField(type MyType, param idx: int) type
proc getField(type MyType, param name: string) type

I could see how it these functions could be confusing, and perhaps the name should be getFieldType. But I do think this is useful functionality to include in the Reflection module.