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List:       groovy-user
Subject:    Re: [groovy-user] Map key confusion
From:       "Steven Devijver" <steven.devijver () gmail ! com>
Date:       2007-01-29 18:48:47
Message-ID: 44b81f710701291048w4475f520xf50b8f2f7ec09b6f () mail ! gmail ! com
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Ok, I got this output from the groovy 1.0 console:

groovy> a = "key"

Result: "key"
groovy> map = [:]

Result: [:]
groovy> map[a] = "value"

Result: "value"
groovy> map[b] = "value"

Exception thrown: groovy.lang.MissingPropertyException: No such
property: b for class: Script3

groovy.lang.MissingPropertyException: No such property: b for class: Script3
	at groovy.lang.MetaClassImpl.getProperty(MetaClassImpl.java:888)
	at groovy.lang.MetaClassImpl.getProperty(MetaClassImpl.java:2077)
	at groovy.lang.GroovyObjectSupport.getProperty(GroovyObjectSupport.java:65)
	at groovy.lang.Script.getProperty(Script.java:85)
	at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.getGroovyObjectProperty(ScriptBytecodeAdapter.java:560)
  at Script3.run(Script3:1)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:484)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:425)
	at gjdk.groovy.lang.GroovyShell_GroovyReflector.invoke(Unknown Source)
	at groovy.lang.MetaMethod.invoke(MetaMethod.java:115)
	at org.codehaus.groovy.runtime.MetaClassHelper.doMethodInvoke(MetaClassHelper.java:713)
  at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:560)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:450)
	at org.codehaus.groovy.runtime.Invoker.invokeMethod(Invoker.java:131)
	at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:111)
	at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodN(ScriptBytecodeAdapter.java:187)
  at groovy.ui.Console$_runScript_closure10.doCall(Console.groovy:503)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:585)
	at org.codehaus.groovy.runtime.ReflectionMetaMethod.invoke(ReflectionMetaMethod.java:69)
  at org.codehaus.groovy.runtime.MetaClassHelper.doMethodInvoke(MetaClassHelper.java:713)
  at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:560)
	at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnCurrentN(ScriptBytecodeAdapter.java:97)
  at groovy.ui.Console$_runScript_closure10.doCall(Console.groovy)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:585)
	at org.codehaus.groovy.runtime.ReflectionMetaMethod.invoke(ReflectionMetaMethod.java:69)
  at org.codehaus.groovy.runtime.MetaClassHelper.doMethodInvoke(MetaClassHelper.java:713)
  at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:560)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:450)
	at groovy.lang.Closure.call(Closure.java:188)
	at groovy.lang.Closure.call(Closure.java:183)
	at groovy.lang.Closure.run(Closure.java:264)
	at java.lang.Thread.run(Thread.java:595)

groovy> map.a = "value2"

Result: "value2"
groovy> println(map)

["key":"value", "a":"value2"]
groovy> map.b = "value2"

Result: "value2"
groovy> map = [ a : "value1", (a) : "value2", b : "value3" ]

Result: ["key":"value2", "b":"value3", "a":"value1"]
groovy> println(map)

["key":"value2", "b":"value3", "a":"value1"]


I guess what was confusing me is that keys are evaluated when creating
entries one an existing map with square brackets. I don't see why we
need this for we have parentheses if we want evaluation.

At least in grails evaluation is much less common than strings as
keys. I now have a much better understanding of how map keys work in
groovy.

Thanks for your feedback.

Steven

On 1/29/07, Russel Winder <russel@russel.org.uk> wrote:
> On Mon, 2007-01-29 at 09:55 +0100, Steven Devijver wrote:
> 
> > Thanks for clarifying. I wouldn't go as far as saying it makes sense
> > but at least I know how to avoid the error.
> 
> Steven,
> 
> What would make sense for you?  If you can show a couple of examples of
> what makes sense for you, I can have a go at trying to explain the
> difference between that and Groovy as is which may help understanding
> for you.
> 
> Speaking from a position of deep ignorance about this implementation
> issues :-) I think the automated stringification of the key in a map
> literal is required for some of the higher builder magic.
> --
> Russel.
> ====================================================
> Dr Russel Winder                +44 20 7585 2200
> 41 Buckmaster Road              +44 7770 465 077
> London SW11 1EN, UK             russel@russel.org.uk
> 
> 
> 

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