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https://issues.apache.org/jira/browse/GROOVY-12399?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King updated GROOVY-12399:
-------------------------------
Affects Version/s: 6.0.0-RC-2
> Arrow switch statement without default throws IllegalStateException when no
> arm matches
> ---------------------------------------------------------------------------------------
>
> Key: GROOVY-12399
> URL: https://issues.apache.org/jira/browse/GROOVY-12399
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 6.0.0-RC-2
> Reporter: Paul King
> Priority: Major
>
> Since GROOVY-12255 (first-class switch expressions), a {{switch}} used as a
> *statement* is only rewritten to a {{SwitchStatement}} when an arrow arm is a
> block that does not {{yield}}. A single expression arm, or a block containing
> exactly one expression statement, becomes an implicit {{yield}} and the
> switch stays a {{SwitchExpression}} even though its value is discarded. Such
> a switch now inherits the expression rules: an unmatched selector throws
> {{IllegalStateException}} in dynamic code and a missing {{default}} is a
> compile error under {{@TypeChecked}} / {{@CompileStatic}}.
> {code:groovy}
> def f(Object o) {
> def r = 'none'
> switch (o) {
> case String -> r = 'str'
> }
> r
> }
> f(42)
> {code}
> Groovy 5.1.2: returns {{'none'}}. Groovy 6.0.0-RC-1:
> {noformat}
> java.lang.IllegalStateException: the switch expression does not cover the
> value 42
> {noformat}
> With {{@TypeChecked}} on {{f}}:
> {noformat}
> the switch expression does not cover all possible input values
> {noformat}
> The boundary depends on arm shape rather than position, which shows it is not
> intended:
> {code:groovy}
> switch (o) { case String -> r = 'str' } // throws when unmatched
> switch (o) { case String -> { r = 'str' } } // throws when unmatched
> switch (o) { case String -> { r = 'str'; r += '!' } } // fine
> switch (o) { case String -> { if (o) r = 'str' } } // fine
> switch (o) { case String: r = 'str' } // fine
> {code}
> The GROOVY-12255 compatibility notes describe the new
> {{IllegalStateException}} and the exhaustiveness error for switch
> _expressions_ only, and state that a switch used as a statement is a
> {{SwitchStatement}}. The statement-position tests in {{Groovy12255.groovy}}
> all carry a {{default}} or always match, so the unmatched case was never
> exercised.
> h3. Proposed fix
> In statement position always build a {{SwitchStatement}}, whatever the arm
> shape ({{isSwitchUsedAsStatement}} already identifies the position). The
> exhaustiveness error and the unmatched-selector throw stay reserved for
> switches whose value is used.
> One case needs a decision: a switch as the last statement of a method body is
> an implicit return value. 4.x/5.x returned the matched arm's value, or
> {{null}} when unmatched. Keeping it an expression preserves the value but
> throws when unmatched; treating it as a statement returns {{null}} in both
> cases.
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