Trying the "structcmp" experiment | CUE

Jonathan Matthews

language

Requires CUE v0.14.0 or later

CUE v0.14.0 introduced the structcmp experiment, which allows both forms of the == operator to compare structs. The experiment needs to be enabled on a per-file basis, and behaves like this:

@experiment(structcmp) // Enable the experiment.
package example

// The comparison operator can now compare
// concrete structs.
output: {
	"a == a": a == a
	"a == b": a == b
	"a == c": a == c
	"a == d": a == d
}

// The unary operator can now assert that one
// struct has the same concrete value as another.
a: ==b

a: foo: 1
b: foo: 1
c: {foo: 1, bar: 1}
d: foo: 2

$ cue export -e output
{
    "a == a": true,
    "a == b": true,
    "a == c": false,
    "a == d": false
}

The == operator requires concrete operands, otherwise evaluation fails:

@experiment(structcmp)
package example

A: foo:  1
_B: foo: int

A: ==_B
C: A == _B

$ cue export
A: invalid right-hand value to '==' (type struct): _B.foo: incomplete value int:
    ./file.cue:7:4

Reference: cue help experiments

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