int[] iv = [1, 2, 3];
// Assigning `int[]` to `any[]` is allowed.
// - set of values allowed by `int` is subset of set of values allowed by `any`
// - set of values allowed by `int[]` is subset of set of values allowed by `any[]`
any[] av = iv;
public function main() {
// A runtime error or else `iv[0]` would have the wrong type.
av[0] = "str";
}
CovarianceArrays and maps are covariant. Static type-checking guarantees that the result of a read from a mutable structure will be consistent with the static type. Covariance means that a write to a mutable structure may result in a runtime error. Arrays, maps, and records have an “inherent” type that constrains mutation. |
int[] iv = [1, 2, 3];
any[] av = iv;
Assigning int[] to any[] is allowed.
- set of values allowed by int is subset of set of values allowed by any
- set of values allowed by int[] is subset of set of values allowed by any[]
public function main() {
av[0] = "str";
A runtime error or else iv[0] would have the wrong type.
}
bal run covariance.bal
error: {ballerina/lang.array}InherentTypeViolation {"message":"incompatible types: expected 'int', found 'string'"}
at covariance:main(covariance.bal:10)
