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Types and are Values

Basic Types

CUE defines the following basic types

null
bool
string
bytes
int
float

in addition to the error type mentioned in the previous section.

CUE does not distinguish between types and values. A field value can be a type (using one of the above names), a concrete value, or, in case of composite types (lists and structs), anything in between.

In the example, point defines an arbitrary point, while xaxis and yaxis define the points on the respective lines. We say that point, xaxis, and yaxis are abstract points, as these points are underspecified. Such abstract values cannot be represented as JSON, which requires all values to be concrete.

The only concrete point is origin. The origin is defined to be both on the x-axis and y-axis, which means it must be at 0, 0. Here we see constraints in action: origin evalutes to 0, 0, even though we did not specify its coordinates explicitly.

types.cue:

point: {
    x: number
    y: number
}

xaxis: point
xaxis x: 0

yaxis: point
yaxis y: 0

origin: xaxis & yaxis

$ cue eval types.cue

point: {
    x: number
    y: number
}
xaxis: {
    x: 0
    y: number
}
yaxis: {
    x: number
    y: 0
}
origin: {
    x: 0
    y: 0
}