upgraded-array-element-type typespec &optional environment → upgraded-typespec

typespec — a type specifier.

environment — an environment object. The default is nil, denoting the null lexical environment and the current global environment.

upgraded-typespec — a type specifier.

Returns the element type of the most specialized array representation capable of holding items of the type denoted by typespec.

The typespec is a subtype of (and possibly type equivalent to) the upgraded-typespec.

If typespec is bit, the result is type equivalent to bit. If typespec is base-char, the result is type equivalent to base-char. If typespec is character, the result is type equivalent to character.

The purpose of upgraded-array-element-type is to reveal how an implementation does its upgrading.

The environment is used to expand any derived type specifiers that are mentioned in the typespec.

array-element-type, make-array

Except for storage allocation consequences and dealing correctly with the optional environment argument, upgraded-array-element-type could be defined as:

(defun upgraded-array-element-type (type &optional environment) 
  (array-element-type (make-array 0 :element-type type)))