tree 1eced088525ea798fce03070c4169feab694acf6
parent 412e5ffd86449be44e3ef9abac278a404b919ec6
author Marcel van Lohuizen <mpvl@golang.org> 1554563943 +0200
committer Marcel van Lohuizen <mpvl@google.com> 1556043360 +0000

doc/ref: refine default values, references and evaluation

The current spec allows for an interpretation that makes default values not commutative:

A: *0 | 1
A: C - B
B: *0 | 1
B: C - A
C: 1

could evaluate to {A: 0, B: 1, C: 1} or {A: 1, B:0, C:1}

With the refined semantics, there is only one interpretation. Expressed in terms of value-default pairs:

A: (0|1 & 1-B, 0 & 1-B) => (0|1 & 1-B, _|_)
B: (0|1 & 1-A, 0 & 1-A) => (0|1 & 1-A, _|_)
C: 1

This updated spec also clarifies how references are resolved.

It also now officially allows an integer literal to be used as an index value.

Note there is now no point during evaluation anymore where a default value is taken over the regular value. Defaults are now only selected over another value when reading a configuration after full evaluation.

Change-Id: Iaea62a5d41c49889f4b5395027bab19e892f166b
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/1784
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>