16 Structs🔗ℹ

In addition to the indicated fields, the hash code function also depends on a random seed and the name of the struct type. A new random seed is generated for each instantiation of the scramble/struct module.

If prop:auto-equal+hash is attached to a struct type that has a super struct type, then the super struct type must also have the prop:auto-equal+hash, and the new equality and hash code functions extend the super type’s functions. If the super struct type does not have the prop:auto-equal+hash property, an error is raised.

> (struct point (x y)     #:property prop:auto-equal+hash #t)

> (equal-hash-code (point 1 2))

980885731491602527

> (equal? (point 1 2) (point 1 2))

#t

> (equal? (point 1 2) (point 0 0))

#f

In the following example, the equality and hash code functions of the point3 struct type use only the z field out of point3’s fields, disregarding the color field, but they also use both of point’s fields.

> (struct point3 point (z color)     #:property prop:auto-equal+hash (list (struct-field-index z)))

> (equal? (point3 1 2 3 #f)           (point3 1 2 3 'red))

#t

> (equal? (point3 0 0 3 'red)           (point3 1 2 3 'red))

#f

> (equal? (equal-hash-code (point3 1 2 3 #f))           (equal-hash-code (point3 1 2 3 'red)))

#t

If prop:auto-custom-write is attached to a struct type that has a super struct type and if that super struct type also has the prop:auto-custom-write property, then the new printer includes the super-type’s fields.

> (struct point (x y) #:property prop:auto-custom-write #t)

> (point 1 2)

(point 1 2)

> (struct point3 point (z) #:property prop:auto-custom-write #t)

> (point3 1 2 3)

(point3 1 2 3)

Added in version 0.6 of package scramble-lib.