[External] : Re: Primitive type patterns

[forax at univ-mlv.fr]

From: "Brian Goetz" <brian.goetz at oracle.com> 
To: "Remi Forax" <forax at univ-mlv.fr> 
Cc: "amber-spec-experts" <amber-spec-experts at openjdk.java.net> 
Sent: Saturday, February 26, 2022 5:49:08 PM 
Subject: Re: [External] : Re: Primitive type patterns 




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#### Relationship with assignment context 

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That's a huge leap, let's take a step back. 

I see two questions that should be answered first. 
1) do we really want pattern in case of assignment/declaration to support assignment conversions ? 
2) do we want patterns used by the switch or instanceof to follow the exact same rules as patterns used in assignment/declaration ? 

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[...] 


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2) we already know that depending on the context (inside a switch, inside a instanceof, inside an assignment) the rules for pattern are not exactly the same. 

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OMG Remi, would you please stop repeating this incorrect claim. The rules for pattern matching are exactly the same across contexts; the differences are that the contexts get to choose when to try to match, and what to do if nothing matches. 
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if (o instanceof Circle(Point(int x, int y), int radius)) 
means 
if (o instanceof Circle circle) { 
Point center = circle.center(); 
if (center == null) { 
goto end 
} 
int x = center.x(); 
int y = center.y(); 
int radius = circle.radius(); 
end: 
} 

while 
Circle(Point(int x, int y), int radius) = c; 
means 
Point center = circle.center(); 
if (center == null) { 
throw new NPE() 
} 
int x = center.x(); 
int y = center.y(); 
int radius = circle.radius(); 
end: 

In the context of switch or instanceof, a pattern does not have to be total, while in case of a assignment the pattern has to be total, 
so depending on the context, the semantics is different. 

Rémi 

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