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Xbase: type computation of switch's case expressions [message #1552909]

Thu, 08 January 2015 11:42

Lorenzo Bettini

Messages: 1812
Registered: July 2009
Location: Firenze, Italy

Senior Member

Hi

I noted that the XbaseTypeComputer computes the type of the case
expressions without type expectation from the switch expression; it just
does this

ITypeComputationState caseState = casePartState.withNonVoidExpectation();

Is that intentional?

This leads to this code in Xtend to be compiled fine

def sw(char c) {
switch(c) {
case '01' : println(0) // this should be a type mismatch
}
}

it is compiled to this Java code

public Integer sw(final char c) {
Integer _switchResult = null;
boolean _matched = false;
if (!_matched) {
if (Objects.equal(c, "01")) {
_matched=true;
_switchResult = InputOutput.<Integer>println(Integer.valueOf(0));
}
}
return _switchResult;
}

But shouldn't it raise a compilation error saying that it expects a char
instead of a String?

cheers
Lorenzo

--
Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
HOME: http://www.lorenzobettini.it
Xtext Book:
http://www.packtpub.com/implementing-domain-specific-languages-with-xtext-and-xtend/book

HOME: http://www.lorenzobettini.it
TDD Book: https://leanpub.com/tdd-buildautomation-ci
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Re: Xbase: type computation of switch's case expressions [message #1552995 is a reply to message #1552909]

Thu, 08 January 2015 12:40

Sebastian Zarnekow

Messages: 3118
Registered: July 2009

Senior Member

Hi Lorenzo,

Xtend lacks some validation for equality comparison of instances of
provable distinct types. This would detect the bogus case in your snippet.

Generally speaking it is valid to do something along these lines:

def Object someObject() {
return 'string';
}
def String someString() {
return 'string'
}

switch someString() {
case someObject(): println('')
}

Here you see that the expectation would have produced a type mismatch
even though this code is fine at runtime.

Best,
Sebastian
--
Looking for professional support for Xtext, Xtend or Eclipse Modeling?
Go visit: http://xtext.itemis.com

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Re: Xbase: type computation of switch's case expressions [message #1553189 is a reply to message #1552995]

Thu, 08 January 2015 14:57

Lorenzo Bettini

Messages: 1812
Registered: July 2009
Location: Firenze, Italy

Senior Member

On 08/01/2015 13:40, Sebastian Zarnekow wrote:
> Hi Lorenzo,
>
> Xtend lacks some validation for equality comparison of instances of
> provable distinct types. This would detect the bogus case in your snippet.
>
> Generally speaking it is valid to do something along these lines:
>
> def Object someObject() {
> return 'string';
> }
> def String someString() {
> return 'string'
> }
>
> switch someString() {
> case someObject(): println('')
> }
>
> Here you see that the expectation would have produced a type mismatch
> even though this code is fine at runtime.

Hi Sebastian

OK, I see; indeed Xbase switch statement is much more powerful than
Java's one.

In my case (yes, still the stricter Xbase/Java version I'm working on),
I just had to add an additional check in the validator and I get my
desired type mismatch back :)

@Check
def void checkSwitch(XSwitchExpression sw) {
val switchExpressionType = getActualType(sw.^switch)
for (c : sw.cases) {
val caseType = getActualType(c.^case)
if (!switchExpressionType.isAssignableFrom(caseType)) {
error(
String.format("Type mismatch: cannot convert from %s to %s",
caseType.humanReadableName, switchExpressionType.humanReadableName
),
c,
XbasePackage.eINSTANCE.XCasePart_Case,
IssueCodes.INCOMPATIBLE_TYPES
)
}
}
}

cheers
Lorenzo

--
Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
HOME: http://www.lorenzobettini.it
Xtext Book:
http://www.packtpub.com/implementing-domain-specific-languages-with-xtext-and-xtend/book

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