RFR: 8303374: Compiler Implementation for Primitive types in patterns, instanceof, and switch (Preview) [v3]

[Maurizio Cimadamore]

On Mon, 2 Oct 2023 14:47:59 GMT, Aggelos Biboudis <abimpoudis at openjdk.org> wrote:

>> This is the first draft of a patch for Primitive types in patterns, instanceof, and switch (Preview).
>> 
>> Draft spec here: https://cr.openjdk.org/~abimpoudis/instanceof/instanceof-20230913/specs/instanceof-jls.html
>
> Aggelos Biboudis has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge branch 'master' into primitive-patterns
>  - Implement type pairs to exactnessMethod name
>  - Apply suggestions from code review
>    
>    Co-authored-by: Raffaello Giulietti <raffaello.giulietti at oracle.com>
>  - 8303374: Compiler Implementation for Primitive types in patterns, instanceof, and switch (Preview)

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Lower.java line 2929:

> 2927:             // This branch covers true unconditionality for the underlying type as well.
> 2928:             if (types.checkUnconditionallyExact(tree.expr.type, tree.pattern.type) &&
> 2929:                 !(tree.expr.type.isReference() && types.isExactPrimitiveWidening(types.unboxedType(tree.expr.type), tree.pattern.type))) {

Not super sure I get this line: if the expression type is unconditionally exact for the pattern type, shouldn't the test be always `true` ? What is the role of the extra guard after the `&&` ? Also, doesn't unconditionally exact implies that there is convertibility?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/15638#discussion_r1343750620