How to write the type signature of a template function in Chapel

Question

In trying to write an arithmetic mean function, it is perhaps better to write one template function rather than two type specific functions. One can write: proc mean(data: [?] ?T): real but how to restrict T to being int or real.

Also is it possible to define an array that can have either int or real data, i.e. is there a way of expressing union types for array contents?

Answer 1

To restrict the type of T to int or real types of any size you can add a where clause to the function definition:

proc mean(data: [] ?T): real where isIntType(T) || isRealType(T) { ... }

The isIntType and isRealType functions are defined in the Types module: http://chapel.cray.com/docs/latest/modules/standard/Types.html

Chapel supports safe unions and arrays of unions. Unions are described in section 17 of the Chapel language specification: http://chapel.cray.com/docs/latest/_downloads/chapelLanguageSpec.pdf

union IntOrReal {
  var i: int;
  var r: real;
}

var intRealArray: [1..2] IntOrReal;
intRealArray[1].i = 1;
intRealArray[2].r = 2.0;